Abstract:
This hot-dip Zn-alloy-plated steel sheet comprises: a steel sheet; and a hot-dip Zn-alloy-plated layer arranged on a surface of the steel sheet. The entire surface of the hot-dip Zn-alloy-plated layer satisfies the following formula (1): S[Zn(OH) 2 ]/(S[Zn(OH) 2 ]+S[Zn])×100≦40. In formula (1): S[Zn] is the area exhibited by a peak having a center at approximately 1022 eV ascribable to metallic Zn in an intensity profile in XPS analysis of the surface of the hot-dip Zn-alloy-plated layer; and S[Zn(OH) 2 ] is the area exhibited by a peak having a center at approximately 1023 eV ascribable to Zn(OH) 2  in an intensity profile in XPS analysis of the surface of the hot-dip Zn-alloy-plated layer.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a hot-dip Zn alloy-plated steel sheet excellent in blackening resistance and a method of producing the same. 
       BACKGROUND ART 
       [0002]    As a plated steel sheet excellent in corrosion resistance, a hot-dip Zn alloy-plated steel sheet having a base steel sheet with a surface coated with a hot-dip Zn alloy plating layer including Al and Mg is known. The composition of the plating layer of a hot-dip Zn alloy-plated steel sheet includes, for example, 4.0 to 15.0% by mass of Al, 1.0 to 4.0% by mass of Mg, 0.002 to 0.1% by mass of Ti, 0.001 to 0.045% by mass of B, and the balance of Zn and unavoidable impurities. The hot-dip Zn alloy-plated steel sheet includes a plating layer of mixed metal structure of [primary crystal Al] and [single phase Zn] in a matrix of [Al/Zn/Zn 2 Mg ternary eutectic structure], having sufficient corrosion resistance and surface appearance as an industrial product. 
         [0003]    The hot-dip Zn alloy-plated steel sheet described above can be continuously produced by the following steps. First, a base steel sheet (steel strip) is passed through a furnace, dipped in a hot-dip Zn alloy plating bath, and then passed through, for example, a gas wiping apparatus, such that the amount of the molten metal adhered to the surface of the base steel sheet is adjusted to a specified amount. Subsequently, the steel strip with the specified amount of molten metal adhered thereto is passed through an air jet cooler and a mist cooling zone, so that the molten metal is cooled to form a hot-dip Zn alloy plating layer. Further, the steel strip with the hot-dip Zn alloy plating layer is passed through a water quenching zone, so as to come in contact with cooling water. A hot-dip Zn alloy-plated steel sheet is thus obtained. 
         [0004]    The hot-dip Zn alloy-plated steel sheet thus produced, however, allows the surface of the plating layer to be blackened over time in some cases. Since the progress of blackening of a hot-dip Zn alloy-plated steel sheet spoils the appearance with a dark gray color without metallic luster, a method for suppressing the blackening has been needed. 
         [0005]    As a method for preventing the blackening, adjusting the temperature of the surface of a plating layer in the water quenching zone has been proposed (e.g. refer to PTL 1). In the invention described in PTL 1, the temperature of the surface of a plating layer is adjusted at lower than 105° C. when to be contacted with cooling water in the water quenching zone so that blackening of the surface of a plating layer is prevented. Alternatively, instead of the temperature control of the surface of a plating layer at lower than 105° C., readily oxidizable elements (rare earth elements, Y, Zr or Si) are added into a plating bath and the temperature of the surface of a plating layer is adjusted at 105 to 300° C. so that blackening of the surface of the plating layer is prevented. 
       CITATION LIST 
     Patent Literature 
     PTL 1 
       [0000]    
       
         Japanese Patent Application Laid-Open No. 2002-226958 
       
     
       SUMMARY OF INVENTION 
     Technical Problem 
       [0007]    In the invention described in PTL 1, since the surface of a plating layer is required to be cooled to a specified temperature before passed through a water quenching zone, the production of hot-dip Zn alloy-plated steel sheets is restricted in some cases. For example, the feed rate of a plated steel sheet having a large thickness is required to be slow so that the plated steel sheet is cooled to a specified temperature, resulting in reduced productivity. In addition, in the case of adding a readily oxidizable element into a plating bath, the readily oxidizable element tends to form a dross. Consequently, complicated concentration control of the readily oxidizable element is required, resulting in a complicated production process, which has been a problem. 
         [0008]    An object of the present invention is to provide a hot-dip Zn alloy-plated steel sheet excellent in blackening resistance which can be produced without reduction in productivity and without complicated control of the components of a plating bath, and a method of producing the same. 
       Solution to Problem 
       [0009]    The present inventors have found that the problem can be solved by reducing the ratio of Zn(OH) 2  at the surface of a plating layer, and accomplished the present invention through further study. 
         [0010]    The present invention relates to the following hot-dip Zn alloy-plated steel sheet. 
         [0011]    [1] A hot-dip Zn alloy-plated steel sheet comprising: a steel sheet; and a hot-dip Zn alloy plating layer disposed on a surface of the steel sheet, wherein the hot-dip Zn alloy plating layer satisfies, at the whole of a surface of the hot-dip Zn alloy plating layer, the following Equation 1: 
         [0000]    
       
         
           
             
               
                 
                   
                     
                       
                         S 
                          
                         
                           [ 
                           
                             
                               Zn 
                                
                               
                                 ( 
                                 OH 
                                 ) 
                               
                             
                             2 
                           
                           ] 
                         
                       
                       
                         
                           S 
                            
                           
                             [ 
                             
                               
                                 Zn 
                                  
                                 
                                   ( 
                                   OH 
                                   ) 
                                 
                               
                               2 
                             
                             ] 
                           
                         
                         + 
                         
                           S 
                            
                           
                             [ 
                             Zn 
                             ] 
                           
                         
                       
                     
                     × 
                     100 
                   
                   ≤ 
                   40 
                 
               
               
                 
                   ( 
                   
                     Equation 
                      
                     
                         
                     
                      
                     1 
                   
                   ) 
                 
               
             
           
         
       
     
         [0012]    wherein S[Zn] is a peak area derived from metal Zn and centered at approximately 1022 eV in an intensity profile of XPS analysis of the surface of the hot-dip Zn alloy plating layer; and S[Zn(OH) 2 ] is a peak area derived from Zn(OH) 2  and centered at approximately 1023 eV in the intensity profile of XPS analysis of the surface of the hot-dip Zn alloy plating layer. 
         [0013]    [2] The hot-dip Zn alloy-plated steel sheet according to [1], wherein: the hot-dip Zn alloy plating layer comprises 1.0 to 22.0% by mass of Al, 0.1 to 10.0% by mass of Mg, and the balance of the hot-dip Zn alloy plating layer being Zn and unavoidable impurities. 
         [0014]    [3] The hot-dip Zn alloy-plated steel sheet according to [2], wherein: the hot-dip Zn alloy plating layer further comprises at least one selected from the group consisting of 0.001 to 2.0% by mass of Si, 0.001 to 0.1% by mass of Ti, and 0.001 to 0.045% by mass of B. 
         [0015]    The present invention also relates to the following method of producing a hot-dip Zn alloy-plated steel sheet. 
         [0016]    [4] A method of producing a hot-dip Zn alloy-plated steel sheet comprising: dipping a base steel sheet in a hot-dip Zn alloy plating bath to form a hot-dip Zn alloy plating layer on a surface of the base steel sheet; and contacting an aqueous solution containing a water-soluble corrosion inhibitor with the surface of the hot-dip Zn alloy plating layer to cool the base steel sheet and the hot-dip Zn alloy plating layer having a raised temperature through formation of the hot-dip Zn alloy plating layer, 
         [0017]    wherein a temperature of the surface of the hot-dip Zn alloy plating layer when the aqueous solution is to be contacted with the surface of the hot-dip Zn alloy plating layer is equal to or more than 100° C. and equal to or less than a solidifying point of the plating layer; and wherein the aqueous solution containing the water-soluble corrosion inhibitor satisfies the following Equation 2: 
         [0000]    
       
         
           
             
               
                 
                   
                     
                       
                         
                           Z 
                           0 
                         
                         - 
                         
                           Z 
                           1 
                         
                       
                       
                         Z 
                         0 
                       
                     
                     × 
                     100 
                   
                   ≥ 
                   20 
                 
               
               
                 
                   ( 
                   
                     Equation 
                      
                     
                         
                     
                      
                     2 
                   
                   ) 
                 
               
             
           
         
       
     
         [0018]    Z 0  is a corrosion current density of the hot-dip Zn alloy-plated steel sheet measured in a 0.5 M NaCl aqueous solution not containing the water-soluble corrosion inhibitor, and Z 1  is a corrosion current density of the hot-dip Zn alloy-plated steel sheet measured in the aqueous solution containing the water-soluble corrosion inhibitor, in which NaCl is further dissolved so that a final concentration of NaCl is 0.5 M. 
       Advantageous Effects of Invention 
       [0019]    According to the present invention, a hot-dip Zn alloy-plated steel sheet excellent in blackening resistance can be easily produced at high productivity. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0020]      FIG. 1A  is a graph illustrating an exemplary polarization curve of a hot-dip Zn alloy-plated steel sheet in 0.5 M NaCl aqueous solution including no water-soluble corrosion inhibitor; 
           [0021]      FIG. 1B  is a graph illustrating an exemplary polarization curve of a hot-dip Zn alloy-plated steel sheet in 0.5 M NaCl aqueous solution containing a water-soluble corrosion inhibitor; 
           [0022]      FIG. 2A  illustrates an exemplary method for contacting a cooling aqueous solution with the surface of a hot-dip Zn alloy plating layer by a spraying process; 
           [0023]      FIG. 2B  illustrates an exemplary method for contacting a cooling aqueous solution with the surface of a hot-dip Zn alloy plating layer by a dipping process; 
           [0024]      FIGS. 3A and 3B  illustrate the intensity profile of the chemical binding energy corresponding to the 2p orbitals of Zn at the surface of a hot-dip Zn alloy plating layer cooled with use of a cooling water to temporarily form a water film; 
           [0025]      FIGS. 4A and 4B  illustrate the intensity profile of the chemical binding energy corresponding to the 2p orbitals of Al at the surface of a hot-dip Zn alloy plating layer cooled with use of a cooling water to temporarily form a water film; 
           [0026]      FIGS. 5A and 5B  illustrate the intensity profile of the chemical binding energy corresponding to the 2p orbitals of Mg at the surface of a hot-dip Zn alloy plating layer cooled with use of a cooling water to temporarily form a water film; 
           [0027]      FIG. 6  illustrates the intensity profile of the chemical binding energy corresponding to the 2p orbitals of Zn at the surface of a hot-dip Zn alloy plating layer cooled with use of a cooling water, without formation of a water film; 
           [0028]      FIG. 7  illustrates the intensity profile of the chemical binding energy corresponding to the 2p orbitals of Zn at the surface of a hot-dip Zn alloy plating layer cooled with use of a cooling aqueous solution containing V 5+  to temporarily form a water film; 
           [0029]      FIGS. 8A to 8D  illustrate the intensity profile of the chemical binding energy corresponding to the 2p orbitals of Zn at the surface of a plating layer; and 
           [0030]      FIG. 9  is a schematic diagram illustrating the configuration of a part of the production line of a hot-dip Zn alloy-plated steel sheet. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
     Method of Producing Hot-Dip Zn Alloy-Plated Steel Sheet of the Present Invention 
       [0031]    The method of producing a hot-dip Zn alloy-plated steel sheet of the present invention (hereinafter, also referred to as “plated steel sheet”) includes: (1) a first step of forming a hot-dip Zn alloy plating layer (hereinafter, also referred to as “plating layer”) on the surface of a base steel sheet; and (2) a second step of contacting a specified aqueous solution with the surface of the plating layer to cool the base steel sheet and the plating layer at a raised temperature through formation of the plating layer. 
         [0032]    One of the features of the production method of the present invention is that after formation of a hot-dip Zn alloy plating layer, a specified cooling aqueous solution is contacted with the surface of the plating layer so as to suppress blackening of the plating layer. Each of the steps is described as follows. 
         [0033]    (1) First Step 
         [0034]    In the first step, a base steel sheet is dipped in a hot-dip Zn alloy plating bath, so that a hot-dip Zn alloy plating layer is formed on the surface of the base steel sheet. 
         [0035]    First, a base steel sheet is dipped in a hot-dip Zn alloy plating bath, and a specified amount of molten metal is allowed to adhere on the surface of the base steel sheet by gas wiping or the like. 
         [0036]    The type of the base steel sheet is not particularly limited. For example, a steel sheet made of low-carbon steel, medium-carbon steel, high-carbon steel, alloy steel or the like may be used as the base steel sheet. When excellent press formability is required, a steel sheet for deep drawing made of low-carbon Ti-alloyed steel, low-carbon Nb-alloyed steel or the like is preferably used as the base steel sheet. Alternatively, a high-strength steel sheet containing P, Si, Mn and the like may be used. 
         [0037]    The composition of a plating bath may be appropriately selected corresponding to the composition of a hot-dip Zn alloy plating layer to be formed. For example, the plating bath includes 1.0 to 22.0% by mass of Al, 0.1 to 10.0% by mass of Mg, and the balance of Zn and unavoidable impurities. The plating bath may further include at least one selected from the group consisting of 0.001 to 2.0% by mass of Si, 0.001 to 0.1% by mass of Ti, and 0.001 to 0.045% by mass of B. Examples of the hot-dip Zn alloy plating include a molten Zn-0.18% by mass of Al-0.09% by mass of Sb alloy plating, a molten Zn-0.18% by mass of Al-0.06% by mass of Sb alloy plating, a molten Zn-0.18% by mass Al alloy plating, a molten Zn-1% by mass of Al-1% by mass of Mg alloy plating, a molten Zn-1.5% by mass of Al-1.5% by mass of Mg alloy plating, a molten Zn-2.5% by mass of Al-3% by mass of Mg alloy plating, a molten Zn-2.5% by mass of Al-3% by mass of Mg-0.4% by mass of Si alloy plating, a molten Zn-3.5% by mass of Al-3% by mass of Mg alloy plating, a molten Zn-4% by mass of Al-0.75% by mass of Mg alloy plating, a molten Zn-6% by mass of Al-3% by mass of Mg-0.05% by mass of Ti-0.003% by mass of B alloy plating, a molten Zn-6% by mass of Al-3% by mass of Mg-0.02% by mass of Si-0.05% by mass of Ti-0.003% by mass of B alloy plating, a molten Zn-11% by mass of Al-3% by mass of Mg alloy plating, a molten Zn-11% by mass of Al-3% by mass of Mg-0.2% by mass of Si alloy plating, and a molten Zn-55% by mass of Al-1.6% by mass of Si alloy plating. Although blackening of a plating layer can be suppressed by addition of Si as described in PTL 1, blackening of a plating layer can be suppressed without addition of Si in the case of producing a plated steel sheet by the production method of the present invention. 
         [0038]    The adhering amount of the hot-dip Zn alloy plating layer is not specifically limited. The adhering amount of the plating layer may be, for example, approximately 60 to 500 g/m 2 . 
         [0039]    Subsequently, the molten metal adhered to the surface of a base steel sheet is cooled to a temperature equal to or more than 100° C. and equal to or less than the solidifying point of the plating layer so as to be solidified. A plated steel sheet is thus formed, having a plating layer with a composition approximately the same as the composition of the plating bath, on the surface of the base steel sheet. 
         [0040]    (2) Second Step 
         [0041]    In the second step, a specified cooling aqueous solution is contacted with the surface of the hot-dip Zn alloy plating layer, so that the base steel sheet and the plating layer at a raised temperature through formation of the hot-dip Zn alloy plating layer are cooled. From the viewpoint of productivity, the second step is performed preferably by water quenching (water cooling). In this case, the temperature of the surface of the hot-dip Zn alloy plating layer when the cooling aqueous solution is to be contacted with the surface of the hot-dip Zn alloy plating layer is equal to or more than 100° C. and approximately equal to or less than the solidifying point of the plating layer. 
         [0042]    The cooling aqueous solution is formed of an aqueous solution containing a water-soluble corrosion inhibitor, satisfying the following equation 3. The following equation 3 indicates that the cooling aqueous solution has a reduction ratio of the corrosion current density of 20% or more. 
         [0000]    
       
         
           
             
               
                 
                   
                     
                       
                         
                           Z 
                           0 
                         
                         - 
                         
                           Z 
                           1 
                         
                       
                       
                         Z 
                         0 
                       
                     
                     × 
                     100 
                   
                   ≥ 
                   20 
                 
               
               
                 
                   ( 
                   
                     Equation 
                      
                     
                         
                     
                      
                     3 
                   
                   ) 
                 
               
             
           
         
       
     
         [0043]    wherein Z 0  is the corrosion current density of a hot-dip Zn alloy-plated steel sheet, measured in a 0.5 M NaCl aqueous solution containing no water-soluble corrosion inhibitor; and Z 1  is the corrosion current density of a hot-dip Zn alloy-plated steel sheet, measured in the aqueous solution (cooling aqueous solution) containing the water-soluble corrosion inhibitor, with further dissolved NaCl at a final concentration of 0.5 M. 
         [0044]    Although NaCl is added to the cooling aqueous solution to have a final concentration of 0.5 M in the measurement of the corrosion current density in the cooling aqueous solution as described above, the hot-dip Zn alloy-plated steel sheet is cooled with the cooling aqueous solution as it is, without addition of NaCl to the cooling aqueous solution. 
         [0045]    The corrosion current density values Z 0  and Z 1  for use in the equation 3 are obtained from a polarization curve by Tafel extrapolation method. The measurement of the polarization curve is performed using an electrochemical measurement system (HZ-3000, produced by Hokuto Denko Corp.). The corrosion current is calculated using software (data analysis software) attached to the electrochemical measurement system.  FIG. 1A  is a graph illustrating an exemplary polarization curve of a hot-dip Zn alloy-plated steel sheet in 0.5 M NaCl aqueous solution including no water-soluble corrosion inhibitor.  FIG. 1B  is a graph illustrating an exemplary polarization curve of a hot-dip Zn alloy-plated steel sheet in 0.5 M NaCl aqueous solution containing a water-soluble corrosion inhibitor. As shown therein, the corrosion current density in the 0.5 M NaCl aqueous solution containing a water-soluble corrosion inhibitor is at least 20% smaller than the corrosion current density measured in the 0.5 M NaCl aqueous solution containing no water-soluble corrosion inhibitor. 
         [0046]    The method for preparing the aqueous solution (cooling aqueous solution) containing a water-soluble corrosion inhibitor is not specifically limited. For example, a water-soluble corrosion inhibitor capable of reducing the corrosion current density, and a dissolution promoter on an as needed basis, may be dissolved in water (solvent). The type of the water-soluble corrosion inhibitor is not specifically limited as long as capable of reducing the corrosion current density. Examples of the water-soluble corrosion inhibitor include a V compound, a Si compound, and a Cr compound. Preferable examples of the V compound include acetylacetone vanadyl, vanadium acetylacetonate, vanadium oxysulfate, vanadium pentoxide, and ammonium vanadate. Further, preferable examples of the Si compound include sodium silicate. Further, preferable examples of the Cr compound include ammonium chromate and potassium chromate. These water-soluble corrosion inhibitors may be used singly or in combination. The amount of the water-soluble corrosion inhibitor added is selected to satisfy the equation 3. 
         [0047]    In the case of adding a dissolution promoter, the amount of the dissolution promoter added is not specifically limited. For example, 90 to 130 parts by mass of the dissolution promoter may be added to 100 parts by mass of the water-soluble corrosion inhibitor. With an excessively small amount of the dissolution promoter added, the water-soluble corrosion inhibitor cannot be sufficiently dissolved in some cases. On the other hand, with an excessively large amount of the dissolution promoter added, the effect is saturated, resulting in a cost disadvantage. 
         [0048]    Examples of the dissolution promoter include 2-aminoethanol, tetraethylammonium hydroxide, ethylene diamine, 2,2′-iminodiethanol, and 1-amino-2-propanol. 
         [0049]    The method for contacting the cooling aqueous solution with the surface of a hot-dip Zn alloy plating layer is not specifically limited. Examples of the method for contacting the cooling aqueous solution with the surface of a hot-dip Zn alloy plating layer include a spraying process and a dipping process. 
         [0050]      FIGS. 2A and 2B  illustrate exemplary methods for contacting a cooling aqueous solution with the surface of a hot-dip Zn alloy plating layer.  FIG. 2A  illustrates an exemplary method for contacting a cooling aqueous solution with the surface of a hot-dip Zn alloy plating layer by a spraying process.  FIG. 2B  illustrates an exemplary method for contacting a cooling aqueous solution with the surface of a hot-dip Zn alloy plating layer by a dipping process. 
         [0051]    As shown in  FIG. 2A , cooling for spraying process includes a plurality of spray nozzles  110 , squeeze rollers  120  disposed downstream of spray nozzles  110  in the feed direction of a steel strip S, and housing  130  which covers the nozzles and the rollers. Spray nozzles  110  are disposed on both sides of the steel strip S. The steel strip S is cooled by a cooling aqueous solution supplied from spray nozzles  110  such that a water film is temporarily formed on the surface of the plating layer, inside housing  130 . The cooling aqueous solution is then removed with squeeze roller  120 . 
         [0052]    As shown in  FIG. 2B , cooling apparatus  200  for dipping process includes dip tank  210  in which a cooling aqueous solution is stored, dip roller  220  disposed inside dip tank  210 , and squeeze rollers  230  disposed downstream of dip roller  220  in the feed direction of the steel strip S so as to remove the extra cooling aqueous solution adhered to the steel strip S. The steel strip S fed into dip tank  210  is then contacted with the cooling aqueous solution so as to be cooled. The steel strip S is then subjected to a turn of direction by the rotating dip roller  220 , and pulled upward. The cooling aqueous solution is removed with squeeze rollers  230 . 
         [0053]    According to the procedure described above, a hot-dip Zn alloy-plated steel sheet excellent in blackening resistance can be produced. 
         [0054]    The reason is not clear why the production method of the present invention can suppress the temporal blackening at the surface of a plating layer of a hot-dip Zn alloy-plated steel sheet. In the following, a presumed mechanism of the occurrence of blackening of a hot-dip Zn alloy plating layer is described, and then a presumed mechanism of the suppression of blackening is described when a hot-dip Zn alloy-plated steel sheet is produced according to the production method of the present invention. The mechanism of the suppression of blackening, however, is not limited to the hypotheses. 
         [0055]    (Mechanism of Occurrence of Blackening) 
         [0056]    First, the process leading to the presumed mechanisms of the occurrence of blackening of the surface of a plating layer and the suppression of the blackening is described as follows. The present inventors produced a hot-dip Zn alloy-plated steel sheet by forming a hot-dip Zn alloy plating layer having a plating composition including 6% by mass of Al, 3% by mass of Mg, 0.024% by mass of Si, 0.05% by mass of Ti, 0.003% by mass of B, and the balance of Zn on the surface of a base steel sheet, and then temporarily forming a water film from cooling water (in-factory water having a pH of 7.6, at 20° C.) in a water quenching zone for a spraying process. The term “temporarily forming a water film” means a state allowing a water film in contact with the surface of a hot-dip Zn alloy-plated steel sheet to be visually observed for one second or more. On this occasion, the surface temperature of the hot-dip Zn alloy-plated steel sheet was estimated to be approximately 160° C. immediately before formation of the water film from the cooling water. 
         [0057]    The produced hot-dip Zn alloy-plated steel sheet was stored in a room (at a room temperature of 20° C., with a relative humidity of 60%) for one week. After storage for one week, the surface of the hot-dip Zn alloy-plated steel sheet was visually observed. The blackening developed on the whole surface of the hot-dip Zn alloy-plated steel sheet and a dark part where blackening particularly proceeded compared with the periphery was observed. 
         [0058]    Furthermore, for 30 regions randomly selected on the surface of a hot-dip Zn alloy-plated steel sheet immediately after production, the chemical binding states of Zn, Al and Mg were analyzed by XPS analysis (X-ray Photoelectoron Spectroscopy). Then, the analyzed hot-dip Zn alloy-plated steel sheet was stored in a room (at a room temperature of 20° C., with a relative humidity of 60%) for one week. After storage for one week, the surface of the hot-dip Zn alloy-plated steel sheet was visually observed. As a result, a dark part was observed in a part of the hot-dip Zn alloy-plated steel sheet. For the region where the dark part was formed and the region where no dark part was observed (normal part), the XPS analysis results of the hot-dip Zn alloy-plated steel sheet obtained immediately after production were compared. 
         [0059]      FIGS. 3A and 3B  to  FIGS. 5A and 5B  are charts illustrating the XPS analysis results of the hot-dip Zn alloy-plated steel sheet obtained immediately after production for the normal part and the dark part.  FIG. 3A  illustrates the intensity profile of the chemical binding energy corresponding to the 2p orbitals of Zn in a normal part.  FIG. 3B  illustrates the intensity profile of the chemical binding energy corresponding to the 2p orbitals of Zn in a dark part.  FIG. 4A  illustrates the intensity profile of the chemical binding energy corresponding to the 2p orbitals of Al in a normal part.  FIG. 4B  illustrates the intensity profile of the chemical binding energy corresponding to the 2p orbitals of Al in a dark part.  FIG. 5A  illustrates the intensity profile of the chemical binding energy corresponding to the 2p orbitals of Mg in a normal part.  FIG. 5B  illustrates the intensity profile of the chemical binding energy corresponding to the 2p orbitals of Mg in a dark part. 
         [0060]    As shown in  FIG. 3A , in the analysis of Zn in a normal part, a peak derived from metal Zn at approximately 1022 eV and a peak derived from Zn(OH) 2  at approximately 1023 eV having a strength weaker than that of the peak derived from metal Zn were observed. From the analysis results, it is found that Zn is present not only as metal Zn, but also present as hydroxide (Zn(OH) 2 ) in the normal part. From the strength ratio between Zn and Zn(OH) 2 , it is found that the Zn is present in larger amount than Zn(OH) 2  in the normal part. 
         [0061]    On the other hand, as shown in  FIG. 3B , also in the analysis of Zn in a dark part, a peak derived from metal Zn at approximately 1022 eV and a peak derived from Zn(OH) 2  at approximately 1023 eV having a strength stronger than that of the peak derived from metal Zn were observed. From the analysis results, it is found that Zn is present not only as metal Zn, but also present as hydroxide (Zn(OH) 2 ) in the dark part, in the same manner as in the normal part. From the strength ratio between Zn and Zn(OH) 2 , it is found that the Zn(OH) 2  is present in larger amount than Zn in the dark part. 
         [0062]    As shown in  FIGS. 4A and 4B , in the analysis of Al in the normal part and the dark part, a peak derived from metal Al at approximately 72 eV and a peak derived from Al 2 O 3  at approximately 74 eV having a strength weaker than that of the peak derived from metal Al were observed. From the analysis results, it is found that Al is present as metal Al and as oxide (Al 2 O 3 ) in the normal part and the dark part. In both of the normal part and the dark part, Al 2 O 3  is present in larger amount than Al, and no major change in the ratio of presence was observed between the normal part and the dark part. 
         [0063]    As shown in  FIGS. 5A and 5B , in the analysis of Mg in the normal part and the dark part, peaks derived from metal Mg, Mg(OH) 2 , and MgO at approximately 49 to 50 eV were observed. From the analysis results, it is found that Mg is present as metal Mg, as oxide (MgO), and as hydroxide (Mg(OH) 2 ) in the normal part and the dark part. No major change in the ratio of presence of metal Mg, Mg(OH) 2 , and MgO was observed between the normal part and the dark part. 
         [0064]    From the results, it is presumed that the binding state of Zn has an effect on formation of the dark part, i.e., the rate of progress in blackening. Accordingly, it is presumed that the dark part is formed, or blackening is accelerated, due to increase in the presence ratio of Zn(OH) 2 . 
         [0065]    Next, the present inventors produced a hot-dip Zn alloy-plated steel sheet by contacting in-factory water (cooling water) with the surface of the hot-dip Zn alloy plating layer by a mist cooling apparatus, without formation of a water film. The produced hot-dip Zn alloy-plated steel sheet was stored in a room (at a room temperature of 20° C., with a relative humidity of 60%) for one week. After storage for one week, the surface of the hot-dip Zn alloy-plated steel sheet was visually observed. The hot-dip Zn alloy-plated steel sheet had a uniform surface gloss, and no formation of a dark part was observed. The degree of gloss at the surface of the plating layer is approximately the same as in the normal part in the hot-dip Zn alloy-plated steel sheet produced through temporary formation of a water film. 
         [0066]    The surface of the plating layer of the hot-dip Zn alloy-plated steel sheet immediately after production without formation of a water film was then analyzed by XPS analysis.  FIG. 6  illustrates the intensity profile of the chemical binding energy corresponding to the 2p orbitals of Zn. The intensity profiles of Al and Mg are omitted. As shown in  FIG. 6 , a peak derived from metal Zn at approximately 1022 eV and a peak derived from Zn(OH) 2  at approximately 1023 eV were observed, even in the case of contact with cooling water without formation of a water film. From the strength ratio between Zn and Zn(OH) 2 , it is found that the Zn is present in larger amount than Zn(OH) 2  in the normal part. Accordingly, it is presumed that the formation of Zn(OH) 2  is not accelerated even in the case of contact with cooling water when a water film is not formed. 
         [0067]    From the results, it is suggested that the formation of a water film in the cooling step has an effect on the formation of Zn(OH) 2 . In the case of no formation of a water film, Zn(OH) 2  is not easily formed, and it is therefore presumed that the blackening is suppressed. 
         [0068]    As described above, regarding blackening of the plating layer of a hot-dip Zn alloy-plated steel sheet, the present inventors found that: 1) Zn(OH) 2  is formed on the surface of the plating layer through formation of a water film in the cooling step; and 2) blackening tends to occur in a region where Zn(OH) 2  is formed in the surface of the plating layer. Accordingly, the present inventors presume that the mechanism of blackening of the plating layer to be as follows. 
         [0069]    First, when a cooling water comes in contact with the surface of a plating layer at high temperature (e.g. 100° C. or higher), partial elution of Zn from the oxide film on the surface of the plating layer or from the Zn phase in the plating layer occurs. 
         [0000]      Zn→Zn 2+ +2 e   − 
 
         [0070]    A part of oxygen dissolved in the cooling water is reduced to form OH − . 
         [0000]      1/2O 2 +H 2 O+2 e   − →2OH − 
 
         [0071]    Zn 2+  eluted into cooling water bonds with OH −  in the cooling water to form Zn(OH) 2  on the surface of the plating layer. 
         [0000]      Zn 2+ -2OH − →Zn(OH) 2  
 
         [0072]    As time passes, a part of Zn(OH) 2  on the surface of the plating layer forms ZnO through a dehydration reaction. 
         [0000]      Zn(OH) 2 →ZnO+H 2 O
 
         [0073]    Subsequently, oxygen is taken from a part of ZnO by Al and Mg in the plating layer, so that ZnO 1-X  is produced. ZnO 1-X  forms a color center, visually exhibiting a black color. 
         [0074]    (Mechanism for Suppressing Blackening) 
         [0075]    Subsequently, the present inventors produced a hot-dip Zn alloy-plated steel sheet by using an aqueous solution of a V compound (reduction ratio of the corrosion current density: 20% or more) instead of in-factory water so as to temporarily form a water film on the surface of the plating layer in the water quenching zone for a spraying process. On this occasion, the surface temperature of the hot-dip Zn alloy-plated steel sheet immediately before contact with the cooling aqueous solution was estimated to be approximately 160° C. 
         [0076]    The produced hot-dip Zn alloy-plated steel sheet was stored in a room (at a room temperature of 20° C., with a relative humidity of 60%) for one week. After storage for one week, the surface of the hot-dip Zn alloy-plated steel sheet was visually observed. The hot-dip Zn alloy-plated steel sheet had a practically uniform surface gloss, and no formation of a dark part was observed. The hot-dip Zn alloy-plated steel sheet had higher surface gloss in comparison with the normal part in the hot-dip Zn alloy-plated steel sheet produced through temporary formation of a water film using in-factory water. 
         [0077]    Subsequently, the surface of the plating layer of the hot-dip alloy plated steel sheet immediately after production through temporary formation of a water film using the cooling aqueous solution was analyzed by XPS analysis.  FIG. 7  illustrates the intensity profile of the chemical binding energy corresponding to the 2p orbitals of Zn in the normal part in the case of using the cooling aqueous solution. The intensity profiles of Al and Mg are omitted. As shown in  FIG. 7 , a peak derived from metal Zn at approximately 1022 eV and a peak derived from Zn(OH) 2  at approximately 1023 eV were observed, even in the case of using the cooling aqueous solution. From the strength ratio between Zn and Zn(OH) 2 , it is found that the Zn is present in larger amount than Zn(OH) 2 . Accordingly, it is presumed that the formation of Zn(OH) 2  is not accelerated even in the case of temporary formation of a water film when an aqueous solution of the V compound (a reduction ratio of the corrosion current density of 20% or more) is used. 
         [0078]    In the case of using an aqueous solution having a reduction ratio of the corrosion current density of 20% or more as cooling water, the progress rate of the series of reactions involved in the formation of Zn(OH) 2  is reduced. It is presumed that the formation of Zn(OH) 2  is thereby suppressed, resulting in suppressed blackening of the plating layer. 
         [0079]    (Hot-Dip Zn Alloy-Plated Steel Sheet of the Present Invention) 
         [0080]    In the hot-dip Zn alloy-plated steel sheet produced by the production method of the present invention (hot-dip Zn alloy-plated steel sheet of the present invention), the amount of Zn(OH) 2  at the surface of the hot-dip Zn alloy plating layer is small. Accordingly, the hot-dip Zn alloy plating layer satisfies, at the entire surface, the following equation 4. 
         [0000]    
       
         
           
             
               
                 
                   
                     
                       
                         S 
                          
                         
                           [ 
                           
                             
                               Zn 
                                
                               
                                 ( 
                                 OH 
                                 ) 
                               
                             
                             2 
                           
                           ] 
                         
                       
                       
                         
                           S 
                            
                           
                             [ 
                             
                               
                                 Zn 
                                  
                                 
                                   ( 
                                   OH 
                                   ) 
                                 
                               
                               2 
                             
                             ] 
                           
                         
                         + 
                         
                           S 
                            
                           
                             [ 
                             Zn 
                             ] 
                           
                         
                       
                     
                     × 
                     100 
                   
                   ≤ 
                   40 
                 
               
               
                 
                   ( 
                   
                     Equation 
                      
                     
                         
                     
                      
                     4 
                   
                   ) 
                 
               
             
           
         
       
     
         [0081]    wherein S[Zn] is a peak area derived from metal Zn and centered at approximately 1022 eV in an intensity profile of XPS analysis of the surface of the hot-dip Zn alloy plating layer; and S[Zn(OH) 2 ] is a peak area derived from Zn(OH) 2  and centered at approximately 1023 eV in the intensity profile of XPS analysis of the surface of the hot-dip Zn alloy plating layer. 
         [0082]    The equation 4 indicates that the ratio of the peak area derived from Zn(OH) 2  and centered at approximately 1023 eV (hereinafter referred to as “Zn(OH) 2  ratio”) is 40% or less relative to the total of the peak area derived from metal Zn and centered at approximately 1022 eV, and peak area derived from Zn(OH) 2  and centered at approximately 1023 eV in the intensity profile measured in the XPS analysis. 
         [0083]      FIGS. 8A to 8D  illustrate the intensity profile of the chemical binding energy corresponding to the 2p orbitals of Zn at the surface of a plating layer of the hot-dip Zn alloy-plated steel sheet.  FIG. 8A  illustrates the intensity profile with a Zn(OH) 2  ratio of approximately 80%,  FIG. 8B  illustrates the intensity profile with a Zn(OH) 2  ratio of approximately 45%,  FIG. 8C  illustrates the intensity profile with a Zn(OH) 2  ratio of approximately 15%, and  FIG. 8D  illustrates the intensity profile with a Zn(OH) 2  ratio of approximately 10%. A dotted line is the base line, a broken line is the intensity profile derived from metal Zn (a peak centered at approximately 1022 eV), and a solid line is the intensity profile derived from Zn(OH) 2  (a peak centered at approximately 1023 eV). In the hot-dip Zn alloy-plated steel sheet of the present invention, the Zn(OH) 2  ratio is 40% or less over the whole surface of the plating layer as shown in  FIGS. 8C and 8D . 
         [0084]    The XPS analysis of the surface of the plating layer of a hot-dip Zn alloy-plated steel sheet is performed using an XPS analyzer (AXIS Nova, produced by Kratos Group PLC.). The peak area derived from metal Zn and centered at approximately 1022 eV, and the peak area derived from Zn(OH) 2  and centered at approximately 1023 eV are calculated using software (Vision 2) attached to the XPS analyzer. 
         [0085]    The position of the peak derived from metal Zn is precisely at 1021.6 eV, and the position of the peak derived from Zn(OH) 2  is precisely at 1023.3 eV. These values may change in some cases due to characteristics of XPS analysis, contamination of a sample, and charging of a sample. Those skilled in the art, however, are capable of distinguishing the peak derived from metal Zn from the peak derived from Zn(OH) 2 . 
         [0086]    (Production Line) 
         [0087]    The method of producing the hot-dip Zn alloy-plated steel sheet of the present invention described above may be performed, for example, in the following production line. 
         [0088]      FIG. 9  is a schematic diagram illustrating a part of production line  300  of a hot-dip Zn alloy-plated steel sheet. Production line  300  forms a plating layer on the surface of a base steel sheet (steel strip), and can continuously produce hot-dip Zn alloy-plated steel sheets. Production line  300  may further form a chemical conversion coating on the surface of the plating layer on an as needed basis, and can continuously produce plated steel sheets with chemical conversion treatment. 
         [0089]    As shown in  FIG. 9 , production line  300  includes furnace  310 , plating bath  320 , air jet cooler  340 , mist cooling zone  350 , water quenching zone  360 , skin pass mill  370 , and tension leveler  380 . 
         [0090]    The steel strip S fed from a feeding reel not shown in drawing through a predetermined step is heated in furnace  310 . The heated steel strip S is dipped in plating bath  320 , so that molten metal adheres to both sides of the steel strip S. An excess amount of molten metal is then removed with a wiping apparatus having wiping nozzle  330 , allowing a specified amount of molten metal to adhere to the surface of the steel strip S. 
         [0091]    The steel strip S with a specified amount of molten metal adhered thereto is cooled to the solidifying point of the molten metal or lower by air jet cooler  340  or in mist cooling zone  350 . Air jet cooler  340  is a facility for cooling the steel strip S by spraying a gas. Mist cooling zone  350  is a facility for cooling the steel strip S by spraying atomized fluid (e.g. cooling water) and a gas. The molten metal is thereby solidified, so that a hot-dip Zn alloy plating layer is formed on the surface of the steel strip S. When the steel strip s is cooled in mist cooling zone  350 , no water film is formed on the surface of the plating layer. The temperature after cooling is not specifically limited, and may be, for example, 100 to 250° C. 
         [0092]    The hot-dip Zn alloy-plated steel sheet cooled to a specified temperature is further cooled in water quenching zone  360 . Water quench zone  360  is a facility for cooling the steel strip S through contact with a large amount of cooling water in comparison with mist cooling zone  350 , supplying an amount of water to form a temporary water film on the surface of the plating layer. For example, water quenching zone  360  includes headers having 10 flat spray nozzles disposed at intervals of 150 mm in the width direction of the steel strip S, which are disposed in 7 rows in the feeding direction of the base steel sheet S. In water quenching zone  360 , an aqueous solution containing a water-soluble corrosion inhibitor (a reduction ratio of the corrosion current density of 20% or more) is used as cooling aqueous solution. The steel strip S is cooled in water quenching zone  360 , with the cooling aqueous solution in an amount to temporarily form a water film on the surface of the plating layer being supplied. For example, the cooling aqueous solution has a water temperature of approximately 20° C., a water pressure of approximately 2.5 kgf/cm 2 , and a water quantity of approximately 150 m 3 /h. The phrase “a water film is temporarily formed” means a state allowing a water film in contact with a hot-dip Zn alloy-plated steel sheet to be visually observed for approximately one seconds or more. 
         [0093]    The water-cooled hot-dip Zn alloy-plated steel sheet is rolled for thermal refining by skin pass mill  370 , corrected to flat by tension leveler  380 , and then wound onto tension reel  390 . 
         [0094]    When a chemical conversion coating is further formed on the surface of a plating layer, a specified chemical conversion treatment liquid is applied to the surface of the hot-dip Zn alloy-plated steel sheet corrected by tension leveler  380 , with roll coater  400 . The hot-dip Zn alloy-plated steel sheet through the chemical conversion treatment is dried and cooled in drying zone  410  and air cooling zone  420 , and then wound onto tension reel  390 . 
         [0095]    As described above, the hot-dip Zn alloy-plated steel sheet of the present invention has excellent blackening resistance and can be easily produced at high productivity. The method of producing a hot-dip Zn alloy-plated steel sheet of the present invention allows a hot-dip Zn alloy-plated steel sheet having excellent blackening resistance to be easily produced at high productivity, only by contacting a specified cooling aqueous solution with the surface of a hot-dip Zn alloy plating layer. 
         [0096]    The present invention is described in detail with reference to Examples as follows. The present invention is, however, not limited to the Examples. 
       EXAMPLES 
     Experiment 1 
       [0097]    In Experiment 1, the blackening resistance of the hot-dip Zn alloy plating layer of a hot-dip Zn alloy-plated steel sheet cooled by using a cooling water containing a water-soluble corrosion inhibitor was examined 
         [0098]    1. Production of Hot-Dip Zn Alloy-Plated Steel Sheet 
         [0099]    Using production line  300  shown in  FIG. 9 , hot-dip Zn alloy-plated steel sheets were produced. A hot-rolled steel strip with a sheet thickness of 2.3 mm was prepared as base steel sheet (steel strip) S. Plating was applied to the base steel sheet using the plating bath compositions and conditions described in Table 1, so that 14 types of hot-dip Zn alloy-plated steel sheets having different plating layer compositions from each other were produced. The composition of the plating bath and the composition of the plating layer are approximately the same. 
         [0000]    
       
         
               
               
             
               
               
             
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
             
             
               
                   
                   
               
               
                   
                 Plating conditions 
               
             
          
           
               
                   
                 Sheet 
               
             
          
           
               
                   
                 Plating bath composition 
                 Bath 
                 Adhering 
                 passing 
               
               
                 Plating 
                 (balance: Zn) (% by mass) 
                 temperature 
                 amount 
                 speed 
               
             
          
           
               
                 No. 
                 Al 
                 Mg 
                 Si 
                 Ti 
                 B 
                 Sb 
                 (° C.) 
                 (g/m 2 ) 
                 (m/min) 
               
               
                   
               
             
          
           
               
                 1 
                 0.18 
                 — 
                 — 
                 — 
                 — 
                 0.09 
                 430 
                 90 
                 80 
               
               
                 2 
                 0.18 
                 — 
                 — 
                 — 
                 — 
                 0.06 
                 430 
                 90 
                 80 
               
               
                 3 
                 0.18 
                 — 
                 — 
                 — 
                 — 
                 — 
                 430 
                 90 
                 80 
               
               
                 4 
                 1 
                 1 
                 — 
                 — 
                 — 
                 — 
                 430 
                 90 
                 80 
               
               
                 5 
                 1.5 
                 1.5 
                 — 
                 — 
                 — 
                 — 
                 430 
                 90 
                 80 
               
               
                 6 
                 2.5 
                 3 
                 — 
                 — 
                 — 
                 — 
                 430 
                 90 
                 80 
               
               
                 7 
                 2.5 
                 3 
                 0.4 
                 — 
                 — 
                 — 
                 430 
                 90 
                 80 
               
               
                 8 
                 3.5 
                 3 
                 — 
                 — 
                 — 
                 — 
                 430 
                 90 
                 80 
               
               
                 9 
                 4 
                 0.75 
                 — 
                 — 
                 — 
                 — 
                 430 
                 90 
                 80 
               
               
                 10 
                 6 
                 3 
                 — 
                 0.05 
                 0.003 
                 — 
                 430 
                 90 
                 80 
               
               
                 11 
                 6 
                 3 
                 0.02 
                 0.05 
                 0.003 
                 — 
                 430 
                 90 
                 80 
               
               
                 12 
                 11 
                 3 
                 — 
                 — 
                 — 
                 — 
                 450 
                 90 
                 80 
               
               
                 13 
                 11 
                 3 
                 0.2 
                 — 
                 — 
                 — 
                 450 
                 90 
                 80 
               
               
                 14 
                 55 
                 — 
                 1.6 
                 — 
                 — 
                 — 
                 600 
                 90 
                 80 
               
               
                   
               
             
          
         
       
     
         [0100]    In production of a hot-dip Zn alloy-plated steel sheet, the cooling conditions in air jet cooler  340  were changed, such that the temperature of the steel sheet (the surface of plating layer) is adjusted at 80° C., 150° C., or 300° C. immediately before passing through water quenching zone  360 . In water quenching zone  360 , any one of the aqueous solutions described in Table 2 and Table 3 was used as cooling aqueous solution. Each of the cooling aqueous solutions was prepared by dissolving a water-soluble corrosion inhibitor described in Table 2 or Table 3 and a dissolution promoter on an as needed basis dissolved in water with a pH of 7.6, at a specified ratio, and then adjusting the water temperature to 20° C. A cooling aqueous solution No. 42 is a water with a pH of 7.6 containing no water-soluble corrosion inhibitor and no dissolution promoter. The spray apparatus in water quenching zone  360  for use includes headers having 10 flat spray nozzles disposed at intervals of 150 mm in the width direction, which are disposed in 7 rows in the feeding direction of the base steel sheet S. Each of the cooling aqueous solutions supplied from water quenching zone  360  was under conditions with a water pressure of 2.5 kgf/cm 2  and a water quantity of 150 m 3 /h. 
         [0101]    The reduction ratio of corrosion current density of each of the cooling aqueous solutions is also described in Table 2 and Table 3. The reduction ratio of corrosion current density is the value calculated from the equation 3 (refer to  FIGS. 1A and 1B ). The corrosion current density is a value obtained from a polarization curve by Tafel extrapolation method. The reduction ratio of corrosion current density of each of cooling aqueous solutions Nos. 10 to 36 is 20% or more, and the reduction ratio of corrosion current density of each of cooling aqueous solutions Nos. 1 to 9 and Nos. 37 to 42 is less than 20%. 
         [0000]    
       
         
               
               
               
               
             
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                   
                 TABLE 2 
               
             
             
               
                   
                   
               
               
                   
                 Water-soluble corrosion inhibitor (A) 
                 Dissolution promoter (B) 
                 Reduction ratio of 
               
             
          
           
               
                   
                 Cooling 
                   
                 Amount added 
                   
                 Ratio of amount 
                 corrosion current 
               
               
                 Category 
                 water No. 
                 Name 
                 (mg/L) 
                 Name 
                 added (B/A) 
                 density (%) 
               
               
                   
               
             
          
           
               
                 Comparative 
                 1 
                 Sodium silicate 
                 0.1 
                 — 
                 — 
                 3 
               
               
                 Example 
                 2 
                 Vanadium acetylacetonate 
                 0.1 
                 Ethylene diamine 
                 1.1 
                 2 
               
               
                   
                 3 
                 Acetylacetone vanadyl 
                 0.1 
                 Ethylene diamine 
                 1.3 
                 −2 
               
               
                   
                 4 
                 Vanadium oxysulfate 
                 0.1 
                 2-Aminoethanol 
                 10 
                 3 
               
               
                   
                 5 
                 Vanadium pentoxide 
                 0.1 
                 1-Amino-2-propanol 
                 1.1 
                 5 
               
               
                   
                 6 
                 Vanadium pentoxide 
                 0.1 
                 Tetraethylammonium 
                 0.9 
                 −4 
               
               
                   
                   
                   
                   
                 hydroxide 
               
               
                   
                 7 
                 Vanadium pentoxide 
                 0.1 
                 2,2′-Iminodiethanol 
                 0.9 
                 −1 
               
               
                   
                 8 
                 Ammonium chromate 
                 0.1 
                 — 
                 — 
                 2 
               
               
                   
                 9 
                 Potassium chromate 
                 0.1 
                 — 
                 — 
                 3 
               
               
                 Example 
                 10 
                 Sodium silicate 
                 30 
                 — 
                 — 
                 61 
               
               
                   
                 11 
                 Vanadium acetylacetonate 
                 30 
                 Ethylene diamine 
                 1.1 
                 40 
               
               
                   
                 12 
                 Acetylacetone vanadyl 
                 30 
                 Ethylene diamine 
                 1.3 
                 45 
               
               
                   
                 13 
                 Vanadium oxysulfate 
                 30 
                 2-Aminoethanol 
                 10 
                 33 
               
               
                   
                 14 
                 Vanadium pentoxide 
                 30 
                 1-Amino-2-propanol 
                 1.1 
                 57 
               
               
                   
                 15 
                 Vanadium pentoxide 
                 30 
                 Tetraethylammonium 
                 0.9 
                 46 
               
               
                   
                   
                   
                   
                 hydroxide 
               
               
                   
                 16 
                 Vanadium pentoxide 
                 30 
                 2,2′-Iminodiethanol 
                 0.9 
                 43 
               
               
                   
                 17 
                 Ammonium chromate 
                 30 
                 — 
                 — 
                 81 
               
               
                   
                 18 
                 Potassium chromate 
                 30 
                 — 
                 — 
                 72 
               
               
                   
                 19 
                 Sodium silicate 
                 500 
                 — 
                 — 
                 92 
               
               
                   
                 20 
                 Vanadium acetylacetonate 
                 500 
                 Ethylene diamine 
                 1.1 
                 84 
               
               
                   
               
             
          
         
       
     
         [0000]    
       
         
               
               
               
               
             
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                   
                 TABLE 3 
               
             
             
               
                   
                   
               
               
                   
                 Water-soluble corrosion inhibitor (A) 
                 Dissolution promoter (B) 
                 Reduction ratio of 
               
             
          
           
               
                   
                 Cooling 
                   
                 Amount added 
                   
                 Ratio of amount 
                 corrosion current 
               
               
                 Category 
                 water No. 
                 Name 
                 (mg/L) 
                 Name 
                 added (B/A) 
                 density (%) 
               
               
                   
               
             
          
           
               
                 Example 
                 21 
                 Acetylacetone vanadyl 
                 500 
                 Ethylene diamine 
                 1.3 
                 83 
               
               
                   
                 22 
                 Vanadium oxysulfate 
                 500 
                 2-Aminoethanol 
                 10 
                 84 
               
               
                   
                 23 
                 Vanadium pentoxide 
                 500 
                 1-Amino-2-propanol 
                 1.1 
                 84 
               
               
                   
                 24 
                 Vanadium pentoxide 
                 500 
                 Tetraethylammonium 
                 0.9 
                 88 
               
               
                   
                   
                   
                   
                 hydroxide 
               
               
                   
                 25 
                 Vanadium pentoxide 
                 500 
                 2,2′-Iminodiethanol 
                 0.9 
                 85 
               
               
                   
                 26 
                 Ammonium chromate 
                 500 
                 — 
                 — 
                 95 
               
               
                   
                 27 
                 Potassium chromate 
                 500 
                 — 
                 — 
                 97 
               
               
                   
                 28 
                 Sodium silicate 
                 3000 
                 — 
                 — 
                 97 
               
               
                   
                 29 
                 Vanadium acetylacetonate 
                 3000 
                 Ethylene diamine 
                 1.1 
                 91 
               
               
                   
                 30 
                 Acetylacetone vanadyl 
                 3000 
                 Ethylene diamine 
                 1.3 
                 90 
               
               
                   
                 31 
                 Vanadium oxysullate 
                 3000 
                 2-Aminoethanol 
                 10 
                 91 
               
               
                   
                 32 
                 Vanadium pentoxide 
                 3000 
                 1-Amino-2-propanol 
                 1.1 
                 91 
               
               
                   
                 33 
                 Vanadium pentoxide 
                 3000 
                 Tetraethylammonium 
                 0.9 
                 91 
               
               
                   
                   
                   
                   
                 hydroxide 
               
               
                   
                 34 
                 Vanadium pentoxide 
                 3000 
                 2,2′-Iminodiethanol 
                 0.9 
                 93 
               
               
                   
                 35 
                 Ammonium chromate 
                 3000 
                 — 
                 — 
                 99 
               
               
                   
                 36 
                 Potassium chromate 
                 3000 
                 — 
                 — 
                 99 
               
               
                 Comparative 
                 37 
                 Chromium nitrate 
                 500 
                 — 
                 — 
                 −67 
               
               
                 Example 
                 38 
                 Chromium sulfate 
                 800 
                 — 
                 — 
                 −87 
               
               
                   
                 39 
                 Cobalt sulfate 
                 1200 
                 — 
                 — 
                 −125 
               
               
                   
                 40 
                 Vanadium oxysulfate 
                 20000 
                 — 
                 — 
                 −180 
               
               
                   
                 41 
                 Copper chloride 
                 1500 
                 — 
                 — 
                 −80 
               
               
                   
                 42 
                 — 
                 — 
                 — 
                 — 
                 0 
               
               
                   
               
             
          
         
       
     
         [0102]    2. Evaluation of Hot-Dip Zn Alloy-Plated Steel Sheet 
         [0103]    (1) Measurement of Ratio of Zn(OH) 2  on Surface of Plating Layer 
         [0104]    The ratio of Zn(OH) 2  on the surface of plating layer was measured for each of the hot-dip Zn alloy-plated steel sheets, using an XPS analyzer (AXIS Nova, produced by Kratos Group PLC.). The ratio of Zn(OH) 2  was calculated using software (Vision 2) attached to the XPS analyzer. 
         [0105]    (2) Treatment for Accelerating Deterioration of Gloss 
         [0106]    A test piece was cut out from each of the produced hot-dip Zn alloy-plated steel sheets. Each of the test pieces was placed in a thermo-hygrostat (LHU-113, produced by Espec Corp.), and subjected to a treatment for accelerating deterioration of the gloss at a temperature 60° C., with a relative humidity of 90%, for 40 hours. 
         [0107]    (3) Measurement of Degree of Blackening 
         [0108]    The brightness (L* value) at the surface of the plating layer for each of the hot-dip Zn alloy-plated steel sheets was measured before and after the treatment for accelerating deterioration of the gloss. The brightness (L* value) at the surface of the plating layer was measured using a spectroscopic color difference meter (TC-1800, produced by Tokyo Denshoku Co., Ltd), by spectral reflectance measurement in accordance with JIS K 5600. The measurement conditions are as follows: 
         [0109]    Optical condition: d/8° method (double beam optical system) 
         [0110]    Field of view: 2-degree field of view 
         [0111]    Measurement method: reflectometry 
         [0112]    Standard illuminant: C 
         [0113]    Color system: CIELAB 
         [0114]    Measurement wavelength: 380 to 780 nm 
         [0115]    Measurement wavelength interval: 5 nm 
         [0116]    Spectroscope: 1200/mm diffraction grating 
         [0117]    Lighting: halogen lamp (voltage: 12 V, power: 50 W, rating life: 2000 hours) 
         [0118]    Measurement area: 7.25 mm diameter 
         [0119]    Detection element: photomultiplier tube (R928 produced by Hamamatsu Photonics K.K.) 
         [0120]    Reflectance: 0 to 150% 
         [0121]    Measurement temperature: 23° C. 
         [0122]    Standard plate: white 
         [0123]    For each of the plated steel sheets, the evaluation was ranked as “A” for a difference in L* values (ΔL*) between before and after the treatment for accelerating deterioration of the gloss of less than 0.5, “B” for a difference of 0.5 or more and less than 3, and “C” for a difference of 3 or more. It can be determined that a plated steel sheet evaluated as “A” has blackening resistance. 
         [0124]    (4) Evaluation Results 
         [0125]    For each of the plated steel sheets, the relations among the type of the cooling aqueous solution for use, the temperature of the steel sheet (the surface of the plating layer) immediately before cooling in water quenching zone  360 , the ratio of Zn(OH) 2 , and the evaluation results of the degree of blackening are described in Table 4 to Table 7. 
         [0000]    
       
         
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                 TABLE 4 
               
               
                   
               
               
                   
                   
                   
                   
                 Sheet 
                   
                   
               
               
                   
                   
                   
                   
                 temperature 
               
               
                   
                 Test 
                   
                   
                 before water 
               
               
                   
                 piece 
                 Plating 
                 Cooling 
                 cooling 
                 Ratio of 
                 Blackening 
               
               
                 Category 
                 No. 
                 No. 
                 water No. 
                 (° C.) 
                 Zn(OH) 2   
                 test result 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 Comp. Ex. 
                 1 
                 11 
                 1 
                 80 
                 72 
                 B 
               
               
                 Comp. Ex. 
                 2 
                 11 
                 2 
                 80 
                 77 
                 B 
               
               
                 Comp. Ex. 
                 3 
                 11 
                 3 
                 80 
                 72 
                 B 
               
               
                 Comp. Ex. 
                 4 
                 11 
                 4 
                 80 
                 73 
                 B 
               
               
                 Comp. Ex. 
                 5 
                 11 
                 5 
                 80 
                 74 
                 B 
               
               
                 Comp. Ex. 
                 6 
                 11 
                 6 
                 80 
                 70 
                 B 
               
               
                 Comp. Ex. 
                 7 
                 11 
                 7 
                 80 
                 70 
                 B 
               
               
                 Comp. Ex. 
                 8 
                 11 
                 8 
                 80 
                 74 
                 B 
               
               
                 Comp. Ex. 
                 9 
                 11 
                 9 
                 80 
                 70 
                 B 
               
               
                 Ex. 
                 10 
                 11 
                 10 
                 80 
                 21 
                 A 
               
               
                 Ex. 
                 11 
                 11 
                 11 
                 80 
                 28 
                 A 
               
               
                 Ex. 
                 12 
                 11 
                 12 
                 80 
                 26 
                 A 
               
               
                 Ex. 
                 13 
                 11 
                 13 
                 80 
                 30 
                 A 
               
               
                 Ex. 
                 14 
                 11 
                 14 
                 80 
                 28 
                 A 
               
               
                 Ex. 
                 15 
                 11 
                 15 
                 80 
                 25 
                 A 
               
               
                 Ex. 
                 16 
                 11 
                 16 
                 80 
                 28 
                 A 
               
               
                 Ex. 
                 17 
                 11 
                 17 
                 80 
                 16 
                 A 
               
               
                 Ex. 
                 18 
                 11 
                 18 
                 80 
                 15 
                 A 
               
               
                 Ex. 
                 19 
                 11 
                 19 
                 80 
                 9 
                 A 
               
               
                 Ex. 
                 20 
                 11 
                 20 
                 80 
                 14 
                 A 
               
               
                 Ex. 
                 21 
                 11 
                 21 
                 80 
                 16 
                 A 
               
               
                 Ex. 
                 22 
                 11 
                 22 
                 80 
                 16 
                 A 
               
               
                 Ex. 
                 23 
                 11 
                 23 
                 80 
                 14 
                 A 
               
               
                 Ex. 
                 24 
                 11 
                 24 
                 80 
                 15 
                 A 
               
               
                 Ex. 
                 25 
                 11 
                 25 
                 80 
                 13 
                 A 
               
               
                 Ex. 
                 26 
                 11 
                 26 
                 80 
                 4 
                 A 
               
               
                 Ex. 
                 27 
                 11 
                 27 
                 80 
                 5 
                 A 
               
               
                 Ex. 
                 28 
                 11 
                 28 
                 80 
                 6 
                 A 
               
               
                 Ex. 
                 29 
                 11 
                 29 
                 80 
                 5 
                 A 
               
               
                 Ex. 
                 30 
                 11 
                 30 
                 80 
                 5 
                 A 
               
               
                 Ex. 
                 31 
                 11 
                 31 
                 80 
                 3 
                 A 
               
               
                 Ex. 
                 32 
                 11 
                 32 
                 80 
                 5 
                 A 
               
               
                 Ex. 
                 33 
                 11 
                 33 
                 80 
                 4 
                 A 
               
               
                 Ex. 
                 34 
                 11 
                 34 
                 80 
                 3 
                 A 
               
               
                 Ex. 
                 35 
                 11 
                 35 
                 80 
                 5 
                 A 
               
               
                 Ex. 
                 36 
                 11 
                 36 
                 80 
                 5 
                 A 
               
               
                 Comp. Ex. 
                 37 
                 11 
                 37 
                 80 
                 94 
                 C 
               
               
                 Comp. Ex. 
                 38 
                 11 
                 38 
                 80 
                 95 
                 C 
               
               
                 Comp. Ex. 
                 39 
                 11 
                 39 
                 80 
                 94 
                 C 
               
               
                 Comp. Ex. 
                 40 
                 11 
                 40 
                 80 
                 94 
                 C 
               
               
                 Comp. Ex. 
                 41 
                 11 
                 41 
                 80 
                 94 
                 C 
               
               
                 Comp. Ex. 
                 42 
                 11 
                 42 
                 80 
                 78 
                 B 
               
               
                   
               
             
          
         
       
     
         [0000]    
       
         
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                 TABLE 5 
               
               
                   
               
               
                   
                   
                   
                   
                 Sheet 
                   
                   
               
               
                   
                   
                   
                   
                 temperature 
               
               
                   
                 Test 
                   
                   
                 before water 
               
               
                   
                 piece 
                 Plating 
                 Cooling 
                 cooling 
                 Ratio of 
                 Blackening 
               
               
                 Category 
                 No. 
                 No. 
                 water No. 
                 (° C.) 
                 Zn(OH) 2   
                 test result 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 Comp. Ex. 
                 43 
                 11 
                 1 
                 150 
                 88 
                 C 
               
               
                 Comp. Ex. 
                 44 
                 11 
                 2 
                 150 
                 93 
                 C 
               
               
                 Comp. Ex. 
                 45 
                 11 
                 3 
                 150 
                 92 
                 C 
               
               
                 Comp. Ex. 
                 46 
                 11 
                 4 
                 150 
                 91 
                 C 
               
               
                 Comp. Ex. 
                 47 
                 11 
                 5 
                 150 
                 93 
                 C 
               
               
                 Comp. Ex. 
                 48 
                 11 
                 6 
                 150 
                 91 
                 C 
               
               
                 Comp. Ex. 
                 49 
                 11 
                 7 
                 150 
                 91 
                 C 
               
               
                 Comp. Ex. 
                 50 
                 11 
                 8 
                 150 
                 91 
                 C 
               
               
                 Comp. Ex. 
                 51 
                 11 
                 9 
                 150 
                 88 
                 C 
               
               
                 Ex. 
                 52 
                 11 
                 10 
                 150 
                 26 
                 A 
               
               
                 Ex. 
                 53 
                 11 
                 11 
                 150 
                 35 
                 A 
               
               
                 Ex. 
                 54 
                 11 
                 12 
                 150 
                 31 
                 A 
               
               
                 Ex. 
                 55 
                 11 
                 13 
                 150 
                 37 
                 A 
               
               
                 Ex. 
                 56 
                 11 
                 14 
                 150 
                 34 
                 A 
               
               
                 Ex. 
                 57 
                 11 
                 15 
                 150 
                 33 
                 A 
               
               
                 Ex. 
                 58 
                 11 
                 16 
                 150 
                 37 
                 A 
               
               
                 Ex. 
                 59 
                 11 
                 17 
                 150 
                 20 
                 A 
               
               
                 Ex. 
                 60 
                 11 
                 18 
                 150 
                 19 
                 A 
               
               
                 Ex. 
                 61 
                 11 
                 19 
                 150 
                 11 
                 A 
               
               
                 Ex. 
                 62 
                 11 
                 20 
                 150 
                 18 
                 A 
               
               
                 Ex. 
                 63 
                 11 
                 21 
                 150 
                 20 
                 A 
               
               
                 Ex. 
                 64 
                 11 
                 22 
                 150 
                 20 
                 A 
               
               
                 Ex. 
                 65 
                 11 
                 23 
                 150 
                 19 
                 A 
               
               
                 Ex. 
                 66 
                 11 
                 24 
                 150 
                 19 
                 A 
               
               
                 Ex. 
                 67 
                 11 
                 25 
                 150 
                 16 
                 A 
               
               
                 Ex. 
                 68 
                 11 
                 26 
                 150 
                 5 
                 A 
               
               
                 Ex. 
                 69 
                 11 
                 27 
                 150 
                 6 
                 A 
               
               
                 Ex. 
                 70 
                 11 
                 28 
                 150 
                 7 
                 A 
               
               
                 Ex. 
                 71 
                 11 
                 29 
                 150 
                 6 
                 A 
               
               
                 Ex. 
                 72 
                 11 
                 30 
                 150 
                 6 
                 A 
               
               
                 Ex. 
                 73 
                 11 
                 31 
                 150 
                 4 
                 A 
               
               
                 Ex. 
                 74 
                 11 
                 32 
                 150 
                 6 
                 A 
               
               
                 Ex. 
                 75 
                 11 
                 33 
                 150 
                 6 
                 A 
               
               
                 Ex. 
                 76 
                 11 
                 34 
                 150 
                 3 
                 A 
               
               
                 Ex. 
                 77 
                 11 
                 35 
                 150 
                 5 
                 A 
               
               
                 Ex. 
                 78 
                 11 
                 36 
                 150 
                 6 
                 A 
               
               
                 Comp. Ex. 
                 79 
                 11 
                 37 
                 150 
                 95 
                 C 
               
               
                 Comp. Ex. 
                 80 
                 11 
                 38 
                 150 
                 95 
                 C 
               
               
                 Comp. Ex. 
                 81 
                 11 
                 39 
                 150 
                 96 
                 C 
               
               
                 Comp. Ex. 
                 82 
                 11 
                 40 
                 150 
                 97 
                 C 
               
               
                 Comp. Ex. 
                 83 
                 11 
                 41 
                 150 
                 97 
                 C 
               
               
                 Comp. Ex. 
                 84 
                 11 
                 42 
                 150 
                 90 
                 C 
               
               
                   
               
             
          
         
       
     
         [0000]    
       
         
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                 TABLE 6 
               
               
                   
               
               
                   
                   
                   
                   
                 Sheet 
                   
                   
               
               
                   
                   
                   
                   
                 temperature 
               
               
                   
                 Test 
                   
                   
                 before water 
               
               
                   
                 piece 
                 Plating 
                 Cooling 
                 cooling 
                 Ratio of 
                 Blackening 
               
               
                 Category 
                 No. 
                 No. 
                 water No. 
                 (° C.) 
                 Zn(OH) 2   
                 test result 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 Comp. Ex. 
                 85 
                 11 
                 1 
                 300 
                 90 
                 C 
               
               
                 Comp. Ex. 
                 86 
                 11 
                 2 
                 300 
                 95 
                 C 
               
               
                 Comp. Ex. 
                 87 
                 11 
                 3 
                 300 
                 93 
                 C 
               
               
                 Comp. Ex. 
                 88 
                 11 
                 4 
                 300 
                 93 
                 C 
               
               
                 Comp. Ex. 
                 89 
                 11 
                 5 
                 300 
                 95 
                 C 
               
               
                 Comp. Ex. 
                 90 
                 11 
                 6 
                 300 
                 93 
                 C 
               
               
                 Comp. Ex. 
                 91 
                 11 
                 7 
                 300 
                 93 
                 C 
               
               
                 Comp. Ex. 
                 92 
                 11 
                 8 
                 300 
                 91 
                 C 
               
               
                 Comp. Ex. 
                 93 
                 11 
                 9 
                 300 
                 90 
                 C 
               
               
                 Ex. 
                 94 
                 11 
                 10 
                 300 
                 28 
                 A 
               
               
                 Ex. 
                 95 
                 11 
                 11 
                 300 
                 35 
                 A 
               
               
                 Ex. 
                 96 
                 11 
                 12 
                 300 
                 33 
                 A 
               
               
                 Ex. 
                 97 
                 11 
                 13 
                 300 
                 38 
                 A 
               
               
                 Ex. 
                 98 
                 11 
                 14 
                 300 
                 36 
                 A 
               
               
                 Ex. 
                 99 
                 11 
                 15 
                 300 
                 34 
                 A 
               
               
                 Ex. 
                 100 
                 11 
                 16 
                 300 
                 37 
                 A 
               
               
                 Ex. 
                 101 
                 11 
                 17 
                 300 
                 20 
                 A 
               
               
                 Ex. 
                 102 
                 11 
                 18 
                 300 
                 22 
                 A 
               
               
                 Ex. 
                 103 
                 11 
                 19 
                 300 
                 13 
                 A 
               
               
                 Ex. 
                 104 
                 11 
                 20 
                 300 
                 18 
                 A 
               
               
                 Ex. 
                 105 
                 11 
                 21 
                 300 
                 22 
                 A 
               
               
                 Ex. 
                 106 
                 11 
                 22 
                 300 
                 22 
                 A 
               
               
                 Ex. 
                 107 
                 11 
                 23 
                 300 
                 22 
                 A 
               
               
                 Ex. 
                 108 
                 11 
                 24 
                 300 
                 20 
                 A 
               
               
                 Ex. 
                 109 
                 11 
                 25 
                 300 
                 18 
                 A 
               
               
                 Ex. 
                 110 
                 11 
                 26 
                 300 
                 8 
                 A 
               
               
                 Ex. 
                 111 
                 11 
                 27 
                 300 
                 9 
                 A 
               
               
                 Ex. 
                 112 
                 11 
                 28 
                 300 
                 9 
                 A 
               
               
                 Ex. 
                 113 
                 11 
                 29 
                 300 
                 9 
                 A 
               
               
                 Ex. 
                 114 
                 11 
                 30 
                 300 
                 8 
                 A 
               
               
                 Ex. 
                 115 
                 11 
                 31 
                 300 
                 7 
                 A 
               
               
                 Ex. 
                 116 
                 11 
                 32 
                 300 
                 8 
                 A 
               
               
                 Ex. 
                 117 
                 11 
                 33 
                 300 
                 8 
                 A 
               
               
                 Ex. 
                 118 
                 11 
                 34 
                 300 
                 5 
                 A 
               
               
                 Ex. 
                 119 
                 11 
                 35 
                 300 
                 8 
                 A 
               
               
                 Ex. 
                 120 
                 11 
                 36 
                 300 
                 8 
                 A 
               
               
                 Comp. Ex. 
                 121 
                 11 
                 37 
                 300 
                 95 
                 C 
               
               
                 Comp. Ex. 
                 122 
                 11 
                 38 
                 300 
                 96 
                 C 
               
               
                 Comp. Ex. 
                 123 
                 11 
                 39 
                 300 
                 96 
                 C 
               
               
                 Comp. Ex. 
                 124 
                 11 
                 40 
                 300 
                 99 
                 C 
               
               
                 Comp. Ex. 
                 125 
                 11 
                 41 
                 300 
                 99 
                 C 
               
               
                 Comp. Ex. 
                 126 
                 11 
                 42 
                 300 
                 98 
                 C 
               
               
                   
               
             
          
         
       
     
         [0000]    
       
         
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                 TABLE 7 
               
               
                   
               
               
                   
                   
                   
                   
                 Sheet 
                   
                   
               
               
                   
                   
                   
                   
                 temperature 
               
               
                   
                 Test 
                   
                   
                 before water 
               
               
                   
                 piece 
                 Plating 
                 Cooling 
                 cooling 
                 Ratio of 
                 Blackening 
               
               
                 Category 
                 No. 
                 No. 
                 water No. 
                 (° C.) 
                 Zn(OH) 2   
                 test result 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 Comp. Ex. 
                 127 
                 9 
                 1 
                 150 
                 84 
                 C 
               
               
                 Comp. Ex. 
                 128 
                 14 
                 2 
                 150 
                 95 
                 C 
               
               
                 Comp. Ex. 
                 129 
                 2 
                 3 
                 150 
                 89 
                 C 
               
               
                 Comp. Ex. 
                 130 
                 10 
                 4 
                 150 
                 85 
                 C 
               
               
                 Comp. Ex. 
                 131 
                 1 
                 5 
                 300 
                 92 
                 C 
               
               
                 Comp. Ex. 
                 132 
                 12 
                 6 
                 150 
                 90 
                 C 
               
               
                 Comp. Ex. 
                 133 
                 5 
                 7 
                 150 
                 90 
                 C 
               
               
                 Comp. Ex. 
                 134 
                 8 
                 8 
                 300 
                 99 
                 C 
               
               
                 Comp. Ex. 
                 135 
                 13 
                 9 
                 150 
                 91 
                 C 
               
               
                 Ex. 
                 136 
                 3 
                 10 
                 150 
                 28 
                 A 
               
               
                 Ex. 
                 137 
                 10 
                 11 
                 150 
                 32 
                 A 
               
               
                 Ex. 
                 138 
                 4 
                 12 
                 300 
                 29 
                 A 
               
               
                 Ex. 
                 139 
                 13 
                 13 
                 150 
                 38 
                 A 
               
               
                 Ex. 
                 140 
                 7 
                 14 
                 150 
                 34 
                 A 
               
               
                 Ex. 
                 141 
                 12 
                 15 
                 150 
                 33 
                 A 
               
               
                 Ex. 
                 142 
                 9 
                 16 
                 300 
                 37 
                 A 
               
               
                 Ex. 
                 143 
                 7 
                 17 
                 150 
                 20 
                 A 
               
               
                 Ex. 
                 144 
                 5 
                 18 
                 150 
                 20 
                 A 
               
               
                 Ex. 
                 145 
                 12 
                 19 
                 150 
                 10 
                 A 
               
               
                 Ex. 
                 146 
                 9 
                 20 
                 300 
                 19 
                 A 
               
               
                 Ex. 
                 147 
                 4 
                 21 
                 150 
                 22 
                 A 
               
               
                 Ex. 
                 148 
                 1 
                 22 
                 150 
                 21 
                 A 
               
               
                 Ex. 
                 149 
                 14 
                 23 
                 150 
                 19 
                 A 
               
               
                 Ex. 
                 150 
                 3 
                 24 
                 300 
                 17 
                 A 
               
               
                 Ex. 
                 151 
                 10 
                 25 
                 300 
                 15 
                 A 
               
               
                 Ex. 
                 152 
                 8 
                 26 
                 150 
                 5 
                 A 
               
               
                 Ex. 
                 153 
                 13 
                 27 
                 150 
                 7 
                 A 
               
               
                 Ex. 
                 154 
                 10 
                 28 
                 300 
                 7 
                 A 
               
               
                 Ex. 
                 155 
                 6 
                 29 
                 150 
                 6 
                 A 
               
               
                 Ex. 
                 156 
                 12 
                 30 
                 150 
                 6 
                 A 
               
               
                 Ex. 
                 157 
                 5 
                 31 
                 150 
                 5 
                 A 
               
               
                 Ex. 
                 158 
                 9 
                 32 
                 300 
                 6 
                 A 
               
               
                 Ex. 
                 159 
                 1 
                 33 
                 300 
                 5 
                 A 
               
               
                 Ex. 
                 160 
                 2 
                 34 
                 150 
                 3 
                 A 
               
               
                 Ex. 
                 161 
                 13 
                 35 
                 300 
                 6 
                 A 
               
               
                 Ex. 
                 162 
                 6 
                 36 
                 150 
                 6 
                 A 
               
               
                 Comp. Ex. 
                 163 
                 13 
                 37 
                 150 
                 88 
                 C 
               
               
                 Comp. Ex. 
                 164 
                 12 
                 38 
                 150 
                 91 
                 C 
               
               
                 Comp. Ex. 
                 165 
                 10 
                 39 
                 300 
                 103 
                 C 
               
               
                 Comp. Ex. 
                 166 
                 9 
                 40 
                 150 
                 104 
                 C 
               
               
                 Comp. Ex. 
                 167 
                 14 
                 41 
                 300 
                 101 
                 C 
               
               
                 Comp. Ex. 
                 168 
                 13 
                 42 
                 300 
                 90 
                 C 
               
               
                   
               
             
          
         
       
     
         [0126]    As shown in Table 4 to Table 7, in the case of cooling using an aqueous solution with a reduction ratio of corrosion current density of 20% or more, a ratio of Zn(OH) 2  at the surface of a plating layer became 40% or less and blackening resistance was excellent. In contrast, in the case of cooling using an aqueous solution with a reduction ratio of corrosion current density of less than 20%, a ratio of Zn(OH) 2  at the surface of a plating layer became more than 40% and suppression of blackening was insufficient. 
         [0127]    From the results, it is found that cooling using an aqueous solution with a reduction ratio of corrosion current density of 20% or more allows the surface of a plating layer to have a ratio of Zn(OH) 2  of 40% or less, and a plated steel sheet with a plating layer having a ratio of Zn(OH) 2  of 40% or less at the surface of the plating layer is excellent in blackening resistance. 
       Experiment 2 
       [0128]    In Experiment 2, a plating layer was formed on a base steel sheet using each of the plating bath compositions (Nos. 1 to 14) and conditions described in Table 1, so that 14 types of hot-dip Zn alloy-plated steel sheets having different plating layer compositions were produced. In production of the hot-dip Zn alloy-plated steel sheets, each of 42 types of cooling aqueous solutions described in Table 2 and Table 3 was used for cooling in water quenching zone  360 . Furthermore, each of the test pieces was subjected to a chemical conversion treatment under the following chemical conversion treatment conditions A to C. Subsequently, the test piece was subjected to the treatment for accelerating deterioration of the gloss in the same manner as in Experiment 1, for the measurement of blackening resistance. 
         [0129]    In chemical conversion treatment conditions A, ZINCHROME 3387N (chrome concentration: 10 g/L, produced by Nihon Parkerizing Co., Ltd.) was used as chemical conversion treatment liquid. The chemical conversion treatment liquid was applied to have an amount of chromium adhering of 10 mg/m 2  by a spray ringer roll method. 
         [0130]    In chemical conversion treatment conditions B, an aqueous solution containing 50 g/L of magnesium phosphate, 10 g/L of potassium fluorotitanate, and 3 g/L of an organic acid was used as chemical conversion treatment liquid. The chemical conversion treatment liquid was applied to have an amount of metal components adhering of 50 mg/m 2  by a roll coat method. 
         [0131]    In chemical conversion treatment conditions C, an aqueous solution containing 20 g/L of a urethane resin, 3 g/L of ammonium dihydrogen phosphate, and 1 g/L of vanadium pentoxide was used as chemical conversion treatment liquid. The chemical conversion treatment liquid was applied to have a dried film thickness of 2 μm by a roll coat method. 
         [0132]    For each of the plated steel sheets, the relations among the type of the cooling aqueous solution for use, the temperature of the steel sheet (the surface of the plating layer) immediately before cooling in water quenching zone  360 , the ratio of Zn(OH) 2 , and the evaluation results of the degree of blackening are described in Table 8 to Table 11. Since the accurate measurement of the ratio of Zn(OH) 2  after the chemical conversion treatment is difficult, the ratio of Zn(OH) 2  is the same as the measurement value in the case of without chemical conversion treatment (the same as the values in Table 4 to Table 7). 
         [0000]    
       
         
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 8 
               
               
                   
               
               
                   
                   
                   
                   
                 Sheet 
                   
                   
                   
               
               
                   
                   
                   
                   
                 temperature 
               
               
                   
                 Test 
                   
                   
                 before water 
                   
                 Chemical 
               
               
                   
                 piece 
                 Plating 
                 Cooling 
                 cooling 
                 Ratio of 
                 conversion 
                 Blackening 
               
               
                 Category 
                 No. 
                 No. 
                 water No. 
                 (° C.) 
                 Zn(OH) 2   
                 treatment 
                 test result 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 Comp. Ex. 
                 169 
                 11 
                 1 
                 80 
                 72 
                 A 
                 B 
               
               
                 Comp. Ex. 
                 170 
                 11 
                 2 
                 80 
                 77 
                 B 
                 B 
               
               
                 Comp. Ex. 
                 171 
                 11 
                 3 
                 80 
                 72 
                 C 
                 B 
               
               
                 Comp. Ex. 
                 172 
                 11 
                 4 
                 80 
                 73 
                 A 
                 B 
               
               
                 Comp. Ex. 
                 173 
                 11 
                 5 
                 80 
                 74 
                 B 
                 B 
               
               
                 Comp. Ex. 
                 174 
                 11 
                 6 
                 80 
                 70 
                 C 
                 B 
               
               
                 Comp. Ex. 
                 175 
                 11 
                 7 
                 80 
                 70 
                 A 
                 B 
               
               
                 Comp. Ex. 
                 176 
                 11 
                 8 
                 80 
                 74 
                 B 
                 B 
               
               
                 Comp. Ex. 
                 177 
                 11 
                 9 
                 80 
                 70 
                 C 
                 B 
               
               
                 Ex. 
                 178 
                 11 
                 10 
                 80 
                 21 
                 A 
                 A 
               
               
                 Ex. 
                 179 
                 11 
                 11 
                 80 
                 28 
                 B 
                 A 
               
               
                 Ex. 
                 180 
                 11 
                 12 
                 80 
                 26 
                 C 
                 A 
               
               
                 Ex. 
                 181 
                 11 
                 13 
                 80 
                 30 
                 A 
                 A 
               
               
                 Ex. 
                 182 
                 11 
                 14 
                 80 
                 28 
                 B 
                 A 
               
               
                 Ex. 
                 183 
                 11 
                 15 
                 80 
                 25 
                 C 
                 A 
               
               
                 Ex. 
                 184 
                 11 
                 16 
                 80 
                 28 
                 A 
                 A 
               
               
                 Ex. 
                 185 
                 11 
                 17 
                 80 
                 16 
                 B 
                 A 
               
               
                 Ex. 
                 186 
                 11 
                 18 
                 80 
                 15 
                 C 
                 A 
               
               
                 Ex. 
                 187 
                 11 
                 19 
                 80 
                 9 
                 A 
                 A 
               
               
                 Ex. 
                 188 
                 11 
                 20 
                 80 
                 14 
                 B 
                 A 
               
               
                 Ex. 
                 189 
                 11 
                 21 
                 80 
                 16 
                 C 
                 A 
               
               
                 Ex. 
                 190 
                 11 
                 22 
                 80 
                 16 
                 A 
                 A 
               
               
                 Ex. 
                 191 
                 11 
                 23 
                 80 
                 14 
                 B 
                 A 
               
               
                 Ex. 
                 192 
                 11 
                 24 
                 80 
                 15 
                 C 
                 A 
               
               
                 Ex. 
                 193 
                 11 
                 25 
                 80 
                 13 
                 A 
                 A 
               
               
                 Ex. 
                 194 
                 11 
                 26 
                 80 
                 4 
                 B 
                 A 
               
               
                 Ex. 
                 195 
                 11 
                 27 
                 80 
                 5 
                 C 
                 A 
               
               
                 Ex. 
                 196 
                 11 
                 28 
                 80 
                 6 
                 A 
                 A 
               
               
                 Ex. 
                 197 
                 11 
                 29 
                 80 
                 5 
                 B 
                 A 
               
               
                 Ex. 
                 198 
                 11 
                 30 
                 80 
                 5 
                 C 
                 A 
               
               
                 Ex. 
                 199 
                 11 
                 31 
                 80 
                 3 
                 A 
                 A 
               
               
                 Ex. 
                 200 
                 11 
                 32 
                 80 
                 5 
                 B 
                 A 
               
               
                 Ex. 
                 201 
                 11 
                 33 
                 80 
                 4 
                 C 
                 A 
               
               
                 Ex. 
                 202 
                 11 
                 34 
                 80 
                 3 
                 A 
                 A 
               
               
                 Ex. 
                 203 
                 11 
                 35 
                 80 
                 5 
                 B 
                 A 
               
               
                 Ex. 
                 204 
                 11 
                 36 
                 80 
                 5 
                 C 
                 A 
               
               
                 Comp. Ex. 
                 205 
                 11 
                 37 
                 80 
                 94 
                 A 
                 C 
               
               
                 Comp. Ex. 
                 206 
                 11 
                 38 
                 80 
                 95 
                 B 
                 C 
               
               
                 Comp. Ex. 
                 207 
                 11 
                 39 
                 80 
                 94 
                 C 
                 C 
               
               
                 Comp. Ex. 
                 208 
                 11 
                 40 
                 80 
                 94 
                 A 
                 C 
               
               
                 Comp. Ex. 
                 209 
                 11 
                 41 
                 80 
                 94 
                 B 
                 C 
               
               
                 Comp. Ex. 
                 210 
                 11 
                 42 
                 80 
                 78 
                 B 
                 B 
               
               
                   
               
             
          
         
       
     
         [0000]    
       
         
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 9 
               
               
                   
               
               
                   
                   
                   
                   
                 Sheet 
                   
                   
                   
               
               
                   
                   
                   
                   
                 temperature 
               
               
                   
                 Test 
                   
                   
                 before water 
                   
                 Chemical 
               
               
                   
                 piece 
                 Plating 
                 Cooling 
                 cooling 
                 Ratio of 
                 conversion 
                 Blackening 
               
               
                 Category 
                 No. 
                 No. 
                 water No. 
                 (° C.) 
                 Zn(OH) 2   
                 treatment 
                 test result 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 Comp. Ex. 
                 211 
                 11 
                 1 
                 150 
                 88 
                 A 
                 C 
               
               
                 Comp. Ex. 
                 212 
                 11 
                 2 
                 150 
                 93 
                 B 
                 C 
               
               
                 Comp. Ex. 
                 213 
                 11 
                 3 
                 150 
                 92 
                 C 
                 C 
               
               
                 Comp. Ex. 
                 214 
                 11 
                 4 
                 150 
                 91 
                 A 
                 C 
               
               
                 Comp. Ex. 
                 215 
                 11 
                 5 
                 150 
                 93 
                 B 
                 C 
               
               
                 Comp. Ex. 
                 216 
                 11 
                 6 
                 150 
                 91 
                 C 
                 C 
               
               
                 Comp. Ex. 
                 217 
                 11 
                 7 
                 150 
                 91 
                 A 
                 C 
               
               
                 Comp. Ex. 
                 218 
                 11 
                 8 
                 150 
                 91 
                 B 
                 C 
               
               
                 Comp. Ex. 
                 219 
                 11 
                 9 
                 150 
                 88 
                 C 
                 C 
               
               
                 Ex. 
                 220 
                 11 
                 10 
                 150 
                 26 
                 A 
                 A 
               
               
                 Ex. 
                 221 
                 11 
                 11 
                 150 
                 35 
                 B 
                 A 
               
               
                 Ex. 
                 222 
                 11 
                 12 
                 150 
                 31 
                 C 
                 A 
               
               
                 Ex. 
                 223 
                 11 
                 13 
                 150 
                 37 
                 A 
                 A 
               
               
                 Ex. 
                 224 
                 11 
                 14 
                 150 
                 34 
                 B 
                 A 
               
               
                 Ex. 
                 225 
                 11 
                 15 
                 150 
                 33 
                 C 
                 A 
               
               
                 Ex. 
                 226 
                 11 
                 16 
                 150 
                 37 
                 A 
                 A 
               
               
                 Ex. 
                 227 
                 11 
                 17 
                 150 
                 20 
                 B 
                 A 
               
               
                 Ex. 
                 228 
                 11 
                 18 
                 150 
                 19 
                 C 
                 A 
               
               
                 Ex. 
                 229 
                 11 
                 19 
                 150 
                 11 
                 A 
                 A 
               
               
                 Ex. 
                 230 
                 11 
                 20 
                 150 
                 18 
                 B 
                 A 
               
               
                 Ex. 
                 231 
                 11 
                 21 
                 150 
                 20 
                 C 
                 A 
               
               
                 Ex. 
                 232 
                 11 
                 22 
                 150 
                 20 
                 A 
                 A 
               
               
                 Ex. 
                 233 
                 11 
                 23 
                 150 
                 19 
                 B 
                 A 
               
               
                 Ex. 
                 234 
                 11 
                 24 
                 150 
                 19 
                 C 
                 A 
               
               
                 Ex. 
                 235 
                 11 
                 25 
                 150 
                 16 
                 A 
                 A 
               
               
                 Ex. 
                 236 
                 11 
                 26 
                 150 
                 5 
                 B 
                 A 
               
               
                 Ex. 
                 237 
                 11 
                 27 
                 150 
                 6 
                 C 
                 A 
               
               
                 Ex. 
                 238 
                 11 
                 28 
                 150 
                 7 
                 A 
                 A 
               
               
                 Ex. 
                 239 
                 11 
                 29 
                 150 
                 6 
                 B 
                 A 
               
               
                 Ex. 
                 240 
                 11 
                 30 
                 150 
                 6 
                 C 
                 A 
               
               
                 Ex. 
                 241 
                 11 
                 31 
                 150 
                 4 
                 A 
                 A 
               
               
                 Ex. 
                 242 
                 11 
                 32 
                 150 
                 6 
                 B 
                 A 
               
               
                 Ex. 
                 243 
                 11 
                 33 
                 150 
                 6 
                 C 
                 A 
               
               
                 Ex. 
                 244 
                 11 
                 34 
                 150 
                 3 
                 A 
                 A 
               
               
                 Ex. 
                 245 
                 11 
                 35 
                 150 
                 5 
                 B 
                 A 
               
               
                 Ex. 
                 246 
                 11 
                 36 
                 150 
                 6 
                 C 
                 A 
               
               
                 Comp. Ex. 
                 247 
                 11 
                 37 
                 150 
                 95 
                 A 
                 C 
               
               
                 Comp. Ex. 
                 248 
                 11 
                 38 
                 150 
                 95 
                 B 
                 C 
               
               
                 Comp. Ex. 
                 249 
                 11 
                 39 
                 150 
                 96 
                 C 
                 C 
               
               
                 Comp. Ex. 
                 250 
                 11 
                 40 
                 150 
                 97 
                 A 
                 C 
               
               
                 Comp. Ex. 
                 251 
                 11 
                 41 
                 150 
                 97 
                 B 
                 C 
               
               
                 Comp. Ex. 
                 252 
                 11 
                 42 
                 150 
                 90 
                 B 
                 C 
               
               
                   
               
             
          
         
       
     
         [0000]    
       
         
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 10 
               
               
                   
               
               
                   
                   
                   
                   
                 Sheet 
                   
                   
                   
               
               
                   
                   
                   
                   
                 temperature 
               
               
                   
                 Test 
                   
                   
                 before water 
                   
                 Chemical 
               
               
                   
                 piece 
                 Plating 
                 Cooling 
                 cooling 
                 Ratio of 
                 conversion 
                 Blackening 
               
               
                 Category 
                 No. 
                 No. 
                 water No. 
                 (° C.) 
                 Zn(OH) 2   
                 treatment 
                 test result 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 Comp. Ex. 
                 253 
                 11 
                 1 
                 300 
                 90 
                 A 
                 C 
               
               
                 Comp. Ex. 
                 254 
                 11 
                 2 
                 300 
                 95 
                 B 
                 C 
               
               
                 Comp. Ex. 
                 255 
                 11 
                 3 
                 300 
                 93 
                 C 
                 C 
               
               
                 Comp. Ex. 
                 256 
                 11 
                 4 
                 300 
                 93 
                 A 
                 C 
               
               
                 Comp. Ex. 
                 257 
                 11 
                 5 
                 300 
                 95 
                 B 
                 C 
               
               
                 Comp. Ex. 
                 258 
                 11 
                 6 
                 300 
                 93 
                 C 
                 C 
               
               
                 Comp. Ex. 
                 259 
                 11 
                 7 
                 300 
                 93 
                 A 
                 C 
               
               
                 Comp. Ex. 
                 260 
                 11 
                 8 
                 300 
                 91 
                 B 
                 C 
               
               
                 Comp. Ex. 
                 261 
                 11 
                 9 
                 300 
                 90 
                 C 
                 C 
               
               
                 Ex. 
                 262 
                 11 
                 10 
                 300 
                 28 
                 A 
                 A 
               
               
                 Ex. 
                 263 
                 11 
                 11 
                 300 
                 35 
                 B 
                 A 
               
               
                 Ex. 
                 264 
                 11 
                 12 
                 300 
                 33 
                 C 
                 A 
               
               
                 Ex. 
                 265 
                 11 
                 13 
                 300 
                 38 
                 A 
                 A 
               
               
                 Ex. 
                 266 
                 11 
                 14 
                 300 
                 36 
                 B 
                 A 
               
               
                 Ex. 
                 267 
                 11 
                 15 
                 300 
                 34 
                 C 
                 A 
               
               
                 Ex. 
                 268 
                 11 
                 16 
                 300 
                 37 
                 A 
                 A 
               
               
                 Ex. 
                 269 
                 11 
                 17 
                 300 
                 20 
                 B 
                 A 
               
               
                 Ex. 
                 270 
                 11 
                 18 
                 300 
                 22 
                 C 
                 A 
               
               
                 Ex. 
                 271 
                 11 
                 19 
                 300 
                 13 
                 A 
                 A 
               
               
                 Ex. 
                 272 
                 11 
                 20 
                 300 
                 18 
                 B 
                 A 
               
               
                 Ex. 
                 273 
                 11 
                 21 
                 300 
                 22 
                 C 
                 A 
               
               
                 Ex. 
                 274 
                 11 
                 22 
                 300 
                 22 
                 A 
                 A 
               
               
                 Ex. 
                 275 
                 11 
                 23 
                 300 
                 22 
                 B 
                 A 
               
               
                 Ex. 
                 276 
                 11 
                 24 
                 300 
                 20 
                 C 
                 A 
               
               
                 Ex. 
                 277 
                 11 
                 25 
                 300 
                 18 
                 A 
                 A 
               
               
                 Ex. 
                 278 
                 11 
                 26 
                 300 
                 8 
                 B 
                 A 
               
               
                 Ex. 
                 279 
                 11 
                 27 
                 300 
                 9 
                 C 
                 A 
               
               
                 Ex. 
                 280 
                 11 
                 28 
                 300 
                 9 
                 A 
                 A 
               
               
                 Ex. 
                 281 
                 11 
                 29 
                 300 
                 9 
                 B 
                 A 
               
               
                 Ex. 
                 282 
                 11 
                 30 
                 300 
                 8 
                 C 
                 A 
               
               
                 Ex. 
                 283 
                 11 
                 31 
                 300 
                 7 
                 A 
                 A 
               
               
                 Ex. 
                 284 
                 11 
                 32 
                 300 
                 8 
                 B 
                 A 
               
               
                 Ex. 
                 285 
                 11 
                 33 
                 300 
                 8 
                 C 
                 A 
               
               
                 Ex. 
                 286 
                 11 
                 34 
                 300 
                 5 
                 A 
                 A 
               
               
                 Ex. 
                 287 
                 11 
                 35 
                 300 
                 8 
                 B 
                 A 
               
               
                 Ex. 
                 288 
                 11 
                 36 
                 300 
                 8 
                 C 
                 A 
               
               
                 Comp. Ex. 
                 289 
                 11 
                 37 
                 300 
                 95 
                 A 
                 C 
               
               
                 Comp. Ex. 
                 290 
                 11 
                 38 
                 300 
                 96 
                 B 
                 C 
               
               
                 Comp. Ex. 
                 291 
                 11 
                 39 
                 300 
                 96 
                 C 
                 C 
               
               
                 Comp. Ex. 
                 292 
                 11 
                 40 
                 300 
                 99 
                 A 
                 C 
               
               
                 Comp. Ex. 
                 293 
                 11 
                 41 
                 300 
                 99 
                 B 
                 C 
               
               
                 Comp. Ex. 
                 294 
                 11 
                 42 
                 300 
                 98 
                 B 
                 C 
               
               
                   
               
             
          
         
       
     
         [0000]    
       
         
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 11 
               
               
                   
               
               
                   
                   
                   
                   
                 Sheet 
                   
                   
                   
               
               
                   
                   
                   
                   
                 temperature 
               
               
                   
                 Test 
                   
                   
                 before water 
                   
                 Chemical 
               
               
                   
                 piece 
                 Plating 
                 Cooling 
                 cooling 
                 Ratio of 
                 conversion 
                 Blackening 
               
               
                 Category 
                 No. 
                 No. 
                 water No. 
                 (° C.) 
                 Zn(OH) 2   
                 treatment 
                 test result 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 Comp. Ex. 
                 295 
                 9 
                 1 
                 150 
                 84 
                 A 
                 C 
               
               
                 Comp. Ex. 
                 296 
                 14 
                 2 
                 150 
                 95 
                 B 
                 C 
               
               
                 Comp. Ex. 
                 297 
                 2 
                 3 
                 150 
                 89 
                 C 
                 C 
               
               
                 Comp. Ex. 
                 298 
                 10 
                 4 
                 150 
                 85 
                 A 
                 C 
               
               
                 Comp. Ex. 
                 299 
                 1 
                 5 
                 300 
                 92 
                 B 
                 C 
               
               
                 Comp. Ex. 
                 300 
                 12 
                 6 
                 150 
                 90 
                 C 
                 C 
               
               
                 Comp. Ex. 
                 301 
                 5 
                 7 
                 150 
                 90 
                 A 
                 C 
               
               
                 Comp. Ex. 
                 302 
                 8 
                 8 
                 300 
                 99 
                 B 
                 C 
               
               
                 Comp. Ex. 
                 303 
                 13 
                 9 
                 150 
                 91 
                 C 
                 C 
               
               
                 Ex. 
                 304 
                 3 
                 10 
                 150 
                 28 
                 A 
                 A 
               
               
                 Ex. 
                 305 
                 10 
                 11 
                 150 
                 32 
                 B 
                 A 
               
               
                 Ex. 
                 306 
                 4 
                 12 
                 300 
                 29 
                 C 
                 A 
               
               
                 Ex. 
                 307 
                 13 
                 13 
                 150 
                 38 
                 A 
                 A 
               
               
                 Ex. 
                 308 
                 7 
                 14 
                 150 
                 34 
                 B 
                 A 
               
               
                 Ex. 
                 309 
                 12 
                 15 
                 150 
                 33 
                 C 
                 A 
               
               
                 Ex. 
                 310 
                 9 
                 16 
                 300 
                 37 
                 A 
                 A 
               
               
                 Ex. 
                 311 
                 7 
                 17 
                 150 
                 20 
                 B 
                 A 
               
               
                 Ex. 
                 312 
                 5 
                 18 
                 150 
                 20 
                 C 
                 A 
               
               
                 Ex. 
                 313 
                 12 
                 19 
                 150 
                 10 
                 A 
                 A 
               
               
                 Ex. 
                 314 
                 9 
                 20 
                 300 
                 19 
                 B 
                 A 
               
               
                 Ex. 
                 315 
                 4 
                 21 
                 150 
                 22 
                 C 
                 A 
               
               
                 Ex. 
                 316 
                 1 
                 22 
                 150 
                 21 
                 A 
                 A 
               
               
                 Ex. 
                 317 
                 14 
                 23 
                 150 
                 19 
                 B 
                 A 
               
               
                 Ex. 
                 318 
                 3 
                 24 
                 300 
                 17 
                 C 
                 A 
               
               
                 Ex. 
                 319 
                 10 
                 25 
                 300 
                 15 
                 A 
                 A 
               
               
                 Ex. 
                 320 
                 8 
                 26 
                 150 
                 5 
                 B 
                 A 
               
               
                 Ex. 
                 321 
                 13 
                 27 
                 150 
                 7 
                 C 
                 A 
               
               
                 Ex. 
                 322 
                 10 
                 28 
                 300 
                 7 
                 A 
                 A 
               
               
                 Ex. 
                 323 
                 6 
                 29 
                 150 
                 6 
                 B 
                 A 
               
               
                 Ex. 
                 324 
                 12 
                 30 
                 150 
                 6 
                 C 
                 A 
               
               
                 Ex. 
                 325 
                 5 
                 31 
                 150 
                 5 
                 A 
                 A 
               
               
                 Ex. 
                 326 
                 9 
                 32 
                 300 
                 6 
                 B 
                 A 
               
               
                 Ex. 
                 327 
                 1 
                 33 
                 300 
                 5 
                 C 
                 A 
               
               
                 Ex. 
                 328 
                 2 
                 34 
                 150 
                 3 
                 A 
                 A 
               
               
                 Ex. 
                 329 
                 13 
                 35 
                 300 
                 6 
                 B 
                 A 
               
               
                 Ex. 
                 330 
                 6 
                 36 
                 150 
                 6 
                 C 
                 A 
               
               
                 Comp. Ex. 
                 331 
                 13 
                 37 
                 150 
                 88 
                 A 
                 C 
               
               
                 Comp. Ex. 
                 332 
                 12 
                 38 
                 150 
                 91 
                 B 
                 C 
               
               
                 Comp. Ex. 
                 333 
                 10 
                 39 
                 300 
                 103 
                 C 
                 C 
               
               
                 Comp. Ex. 
                 334 
                 9 
                 40 
                 150 
                 104 
                 A 
                 C 
               
               
                 Comp. Ex. 
                 335 
                 14 
                 41 
                 300 
                 101 
                 B 
                 C 
               
               
                 Comp. Ex. 
                 336 
                 13 
                 42 
                 300 
                 90 
                 C 
                 C 
               
               
                   
               
             
          
         
       
     
         [0133]    As shown in Table 8 to Table 11, in the case of cooling using an aqueous solution with a reduction ratio of corrosion current density of 20% or more, excellent blackening resistance was obtained even with the chemical conversion treatment. In contrast, in the case of cooling using an aqueous solution with a reduction ratio of corrosion current density of less than 20%, the suppression of blackening was insufficient even with the chemical conversion treatment. 
         [0134]    From the results, it is found that cooling using an aqueous solution with a reduction ratio of corrosion current density of 20% or more can sufficiently suppress blackening regardless of the type of chemical conversion treatment. 
         [0135]    This application claims priority based on Japanese patent Application No. 2013-250143, filed on Dec. 3, 2013, the entire contents of which including the specification and the drawings are incorporated herein by reference. 
       INDUSTRIAL APPLICABILITY 
       [0136]    The hot-dip Zn alloy-plated steel sheet obtained by the production method of the present invention is excellent in blackening resistance, and useful as plated steel sheet for use in, for example, roof materials and exterior materials for buildings, home appliances, and automobiles. 
       REFERENCE SIGNS LIST 
       [0000]    
       
           100 ,  200  Cooling apparatus 
           110  Spray nozzle 
           120 ,  230  Squeeze roll 
           130  Housing 
           210  Dip tank 
           220  Dip roller 
           300  Production line 
           310  Furnace 
           320  Plating bath 
           330  Wiping nozzle 
           340  Air jet cooler 
           350  Mist cooling zone 
           360  Water quenching zone 
           370  Skin pass mill 
           380  Tension leveler 
           390  Tension reel 
           400  Roll coater 
           410  Drying zone 
           420  Air cooling zone 
         S: Steel strip