Patent Publication Number: US-2013244055-A1

Title: Aluminum alloy brazing sheet for heat exchanger

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority from Japanese Patent Application No. 2012-061175, the disclosure of which is incorporated herein by reference in its entirety. 
     BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The present invention relates to an aluminum alloy brazing sheet for heat exchangers used for an automotive heat exchanger, etc. 
     2. Description of the Related Art 
     Generally, as a tube material in an automotive heat exchanger such as an evaporator or a condenser, an aluminum alloy brazing sheet obtained by cladding a core with a sacrificial material and a brazing filler metal (hereinafter sometimes referred to as a brazing sheet) formed into a tube by electric resistance welding has been used. In such a brazing sheet for use as a tube material, an Al—Mn-based alloy, for example, is used as the core, and an Al—Zn-based alloy, for example, is used as the sacrificial material on the inner side, which in one side of the core, i.e., the side that is constantly in contact with a refrigerant. Further, when formed into a tube, an Al—Si-based alloy is usually used as the brazing filler metal on the outer side, which is the other side of the core. 
     In recent years, there is a trend toward lighter and smaller automotive heat exchangers. With this trend, the thinning of a tube material, which occupies a large part of the mass of a heat exchanger, has been desired. For the thinning of a tube material, it is necessary to increase strength and corrosion resistance corresponding to the decrease in thickness. In response to such needs, aluminum alloy brazing sheets and clad materials for achieving high strength, high corrosion resistance, etc., have been proposed. 
     For example, JP-A-2001-170793 discloses a high-strength aluminum alloy clad material for heat exchangers having excellent high frequency weldability and corrosion resistance, characterized in that a core and a sacrificial material are each specified to have a predetermined alloy composition, the matrix of the core has a fiber structure, and the clad material has a tensile strength of 170 to 260 MPa. 
     SUMMARY OF THE INVENTION 
     However, the prior technique has the following problems. 
     As mentioned above, for the thinning of a material, strength and corrosion resistance are increased corresponding to a decrease in thickness, for example. However, thinning causes a problem in that weld defects are increased during the electric resistance welding of a tube material, and further a lot of unexpected welding defects occur. Accordingly, the improvement of high frequency weldability during electric resistance welding (i.e., high frequency welding properties) is required. 
     The present invention has been made in view of the above-mentioned problems. An object of the present invention is to provide an aluminum alloy brazing sheet for heat exchangers having excellent strength and corrosion resistance even when it is formed into a thin material and also having excellent high frequency weldability during electric resistance welding (high frequency welding properties). 
     An aluminum alloy brazing sheet for heat exchangers according to the present invention comprising: a core consisting of an aluminum alloy containing Si: 0.1 to 1.0% by mass, Cu: 0.5 to 1.2% by mass, and Mn: 0.5 to 2.0% by mass, the balance being Al and unavoidable impurities; a sacrificial material provided on one side of the core and made of an aluminum alloy containing Si: more than 0.2% by mass and not more than 0.8% by mass, Zn: more than 2.0% by mass and not more than 5.0% by mass, and Mg: 1.0 to 4.5% by mass with the balance of Al and unavoidable impurities; and a brazing filler metal provided on the other side of the core and made of an aluminum alloy, wherein the aluminum alloy brazing sheet for heat exchangers has a work hardening exponent n of not less than 0.05. 
     According to this configuration, the core contains predetermined amounts of Si, Cu, and Mn, whereby strength after brazing and corrosion resistance are improved, while the sacrificial material contains predetermined amounts of Si, Zn, and Mg, whereby strength after brazing and corrosion resistance are improved. In addition, the work hardening exponent n is not less than 0.05, whereby the inclination in the plastic working range is increased, leading to an increase in the critical value of strain at which buckling occurs. As a result, during the formation of a diminishing pipe by fin pass rolls, the occurrence of buckling at the edge portion is suppressed, and high frequency welding properties are improved. 
     The core may further contain at least one member selected from Ti: 0.05 to 0.25% by mass, Cr: not more than 0.25% by mass, and Mg: 0.05 to 0.5% by mass. 
     According to this configuration, the core contains predetermined amounts of Ti, Cr, and Mg, whereby corrosion resistance and strength after brazing are improved. 
     The aluminum alloy brazing sheet for heat exchangers according to the present invention makes it possible to improve strength and corrosion resistance even in a thin material. Further, high frequency welding properties can also be improved. Accordingly, during the formation of a diminishing pipe by fin pass rolls, the occurrence of buckling at the edge portion can be suppressed, whereby matching during electric resistance welding is stabilized. Therefore, an excellent electric resistance welded tube can be obtained. Further, this makes it possible to reduce the weight and size of a heat exchanger and also cut costs. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view showing a configuration of an aluminum alloy brazing sheet for heat exchangers according to an embodiment of the present invention; 
         FIG. 2  is a cross-sectional view for explaining the buckling of an edge portion of a tube material; and 
         FIG. 3  is an explanatory view for explaining an evaluation test on brazeability in the examples. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, the form of an aluminum alloy brazing sheet for heat exchangers according to an embodiment of the present invention will be described in detail with reference to the drawings. Incidentally, the size, positional relationship, and the like of the members shown in the drawings are sometimes exaggerated for a clear explanation. 
     &lt;&lt;Aluminum Alloy Brazing Sheet for Heat Exchangers&gt;&gt; 
     As shown in  FIG. 1 , an aluminum alloy brazing sheet  1  for heat exchangers (hereinafter sometimes referred to as a brazing sheet) according to an embodiment of the present invention includes a sacrificial material  3  on one side of a core  2  and a brazing filler metal  4  on the other side of the core  2 . Further, the brazing sheet  1  has a work hardening exponent n of not less than 0.05. 
     Hereinafter, each configuration will be described. 
     &lt;Core&gt; 
     The core  2  is an aluminum alloy containing Si: 0.1 to 1.0% by mass, Cu: 0.5 to 1.2% by mass, Mn: 0.5 to 2.0% by mass, and the balance of Al and unavoidable impurities. As optional components, the core  2  may further contain at least one member selected from Ti: 0.05 to 0.25% by mass, Cr: not more than 0.25% by mass, and Mg: 0.05 to 0.5% by mass. 
     [Si: 0.1 to 1.0% by Mass] 
     Si forms an intermetallic compound together with Al and Mn and is finely distributed in the crystal grains to contribute to dispersion strengthening, thereby improving strength after brazing. When the Si content is less than 0.1% by mass, strength after brazing decreases. Meanwhile, when the Si content is more than 1.0% by mass, the solidus temperature of the core  2  decreases. As a result, the core  2  melts during heating for brazing. Therefore, the Si content is specified to be 0.1 to 1.0% by mass. The content is preferably 0.2 to 0.4% by mass. 
     [Cu: 0.5 to 1.2% by Mass] 
     Cu is effective in improving strength after brazing. Further, the addition of Cu leads to a higher potential, increasing the potential difference from the sacrificial material  3 . As a result, corrosion resistance is improved. When the Cu content is less than 0.5% by mass, strength after brazing decreases. In addition, the potential difference from the sacrificial material  3  cannot be ensured, whereby internal corrosion resistance decreases. Meanwhile, when the Cu content is more than 1.2% by mass, the solidus temperature of the core  2  decreases. As a result, the core  2  melts during heating for brazing. Therefore, the Cu content is specified to be 0.5 to 1.2% by mass. The content is preferably more than 0.7% by mass and not more than 1.1% by mass. 
     [Mn: 0.5 to 2.0% by Mass] 
     Mn is effective in improving strength after brazing. When the Mn content is less than 0.5% by mass, the number of intermetallic compounds formed between Al and Si decreases. As a result, the improvement of dispersion strengthening by an intermetallic compound is not achieved, and strength after brazing decreases. Meanwhile, when the content is more than 2.0% by mass, a large number of coarse intermetallic compounds are produced. As a result, rolling itself becomes difficult, making it difficult to produce the brazing sheet  1 . Therefore, the Mn content is specified to be 0.5 to 2.0% by mass. The content is preferably 0.8 to 1.7% by mass. 
     [Ti: 0.05 to 0.25% by Mass] 
     Ti is distributed in the form of layers in the core  2  and greatly improves the corrosion resistance of the inner and outer surfaces. In the case where Ti is added, when the Ti content is less than 0.05% by mass, Ti is not distributed in the form of layers in the core  2 . This results in pitting with significant corrosion, whereby corrosion resistance decreases. Meanwhile, when the content is more than 0.25% by mass, coarse intermetallic compounds are formed during casting, whereby corrosion resistance decreases. Therefore, in the case where Ti is added, the Ti content is specified to be 0.05 to 0.25% by mass. The content is preferably 0.1 to 0.20% by mass. 
     [Cr: not more than 0.25% by Mass] 
     Cr forms an intermetallic compound in the core  2  and is effective in improving strength after brazing. When the Cr content is more than 0.25% by mass, coarse intermetallic compounds are formed during casting, whereby corrosion resistance decreases. Therefore, in the case where Cr is added, the Cr content is specified to be not more than 0.25% by mass. The content is preferably not more than 0.15% by mass. 
     [Mg: 0.05 to 0.5% by Mass] 
     Mg forms a fine Mg 2 Si precipitation phase together with Si and is effective in improving strength after brazing. When the Mg content is less than 0.05% by mass, strength after brazing is not sufficiently improved. Meanwhile, when the content is more than 0.5% by mass, in the case where brazing is performed using a non-corrosive flux, the flux reacts with Mg, making it impossible to perform brazing. Therefore, in the case where Mg is added, the Mg content is specified to be 0.05 to 0.5% by mass. The content is preferably 0.05 to 0.30% by mass. 
     [Balance: Al and Unavoidable Impurities 
     With respect to the components of the core  2  other than the above, the balance is Al and unavoidable impurities. Incidentally, examples of unavoidable impurities include Fe and Zr. They may be contained in the core  2  without interfering with the effect of the present invention as long as their contents are each not more than 0.2% by mass. 
     &lt;Sacrificial Material&gt; 
     The sacrificial material  3  is an aluminum alloy containing Si: more than 0.2% by mass and not more than 0.8% by mass, Zn: more than 2.0% by mass and not more than 5.0% by mass, Mg: 1.0 to 4.5% by mass, and the balance of Al and unavoidable impurities. 
     [Si: More than 0.2% by Mass and not More than 0.8% by Mass] 
     Si diffuses into the core  2  during brazing and is, together with Mg that diffuses from the sacrificial material  3  into the core  2 , effective in precipitating Mg 2 Si in the core  2  after brazing and improving strength after brazing. When the Si content is not more than 0.2% by mass, it is less effective in precipitating Mg 2 Si, and strength after brazing decreases. Meanwhile, when the content is more than 0.8% by mass, the solidus temperature decreases, whereby the sacrificial material  3  melts. Therefore, the Si content is specified to be more than 0.2% by mass and not more than 0.8% by mass. The content is preferably more than 0.2% by mass and not more than 0.6% by mass. 
     [Zn: More than 2.0% by Mass and not More than 5.0% by Mass] 
     Zn is an element that lowers the potential. The addition of Zn to the sacrificial material  3  is effective in ensuring a potential difference from the core  2  and improving internal corrosion resistance. A Zn content of not more than 2.0% by mass leads to a small potential difference from the core  2 , which is insufficient for ensuring internal corrosion resistance. As a result, internal corrosion resistance decreases. Meanwhile, when the content is more than 5.0% by mass, the solidus temperature decreases. As a result, the sacrificial material  3  melts during brazing and becomes unusable as a tube material. Therefore, the Zn content is specified to be more than 2.0% by mass and not more than 5.0% by mass. The content is preferably more than 3.0% by mass and not more than 4.5% by mass. 
     [Mg: 1.0 to 4.5% by Mass] 
     Mg forms a fine Mg 2 Si precipitation phase together with Si and is effective in improving strength after brazing. When the Mg content is less than 1.0% by mass, it is less effective in precipitating Mg 2 Si, and strength after brazing is not sufficiently improved. Meanwhile, when the content is more than 4.5% by mass, the rolling workability significantly deteriorates, making it difficult to produce the brazing sheet  1 . Therefore, the Mg content is specified to be 1.0 to 4.5% by mass. The content is preferably 1.5 to 4.0% by mass. 
     [Balance: Al and Unavoidable Impurities] 
     With respect to the components of the sacrificial material  3  other than the above, the balance is Al and unavoidable impurities. Incidentally, examples of unavoidable impurities include Mn, Cr, Zr, Fe, In, and Sn. They may be contained in the sacrificial material  3  without interfering with the effect of the present invention as long as the Mg content is less than 0.05% by mass, the Cr and Zr contents are each not more than 0.2% by mass, the Fe content is not more than 0.25% by mass, and the In and Sn contents are each not more than 0.1% by mass. 
     &lt;Brazing Filler Metal&gt; 
     The brazing filler metal  4  is made of an Al-based alloy. Examples of the Al-based alloy include ordinary JIS alloys such as 4343 and 4045. Here, Al-based alloys include alloys containing Si and also alloys containing Zn. That is, examples of the Al-based alloy include Al—Si-based alloys and Al—Si—Zn-based alloys. For example, it is possible to use an Al—Si-based alloy containing Si: 7 to 12% by mass. 
     When the Si content is less than 7% by mass, the amount of an Al—Si liquid phase at the brazing temperature is so small that brazeability is likely to deteriorate. Meanwhile, when the content is more than 12% by mass, the amount of coarse primary crystals Si increases during the casting of the brazing filler metal  4 . As a result, when such a brazing filler metal is used in the brazing sheet  1 , excessive melting is likely to occur at the interface between the core  2  and the brazing filler metal  4 , whereby strength after brazing and corrosion resistance are likely to decrease. 
     However, the brazing filler metal  4  is not particularly limited and may be any of ordinary Al-based (Al—Si-based, Al—Si—Zn-based) alloys. In addition, Al—Si—Mg-based and Al—Si—Mg—Bi-based alloys that are used for vacuum brazing are also fully usable. Further, for example, in addition to Si, Zn, Mg, and Bi, Fe, Cu, Mn, and the like may also be contained. 
     &lt;Work Hardening Exponent n: Not Less than 0.05&gt; 
     A work hardening exponent n is a property value that serves as an index of formability. It is known that when the work hardening exponent n is large, strain is easily transmitted, which leads to uniform deformation, resulting in improved elongation until local deformation (uniform elongation). However, it is known that the work hardening exponent of an aluminum alloy changes depending on the amount of strain and is likely to decrease especially in a high strain region (nominal strain: not less than 0.10). 
     In the present invention, it is important that the work hardening exponent n of the brazing sheet  1  before electric resistance welding is not less than 0.05. Extensive research has been conducted on an increase in weld defects during the electric resistance welding of a tube material accompanying thinning, and the process of the formation of an electric resistance welded tube has been fully examined. As a result, it has been found that as shown in  FIG. 2 , when weld defects occur, an edge portion E of a tube material A buckles during the formation of a diminishing pipe at about 2% strain by fin pass rolls. It has also been found that the work hardening exponent n greatly affects such buckling. In plastic working at about 2% strain by fin pass rolls, when the work hardening exponent n of the brazing sheet  1  is not less than 0.05, the inclination in the plastic working range is increased, leading to an increase in the critical value of strain at which buckling occurs. As a result, buckling caused by fin pass rolls can be suppressed, whereby matching during electric resistance welding is stabilized, making it possible to obtain an excellent thin electric resistance welded tube. Therefore, the work hardening exponent n of the brazing sheet  1  is specified to be not less than 0.05. 
     The work hardening exponent n can be calculated by a tensile test on a brazing sheet  1  processed into a test piece JIS No. 5 in accordance with the two-point method of JIS Z 2253 at 2% strain and 6% strain. 
     Further, the work hardening exponent n are controlled by the finish cold rolling reduction and the finish annealing conditions as described in the production method for the brazing sheet  1  later. 
     Such a brazing sheet can be produced by the following production method, for example. 
     First, an aluminum alloy for a core, an aluminum alloy for a sacrificial material, and an aluminum alloy for a brazing filler metal are melted by continuous casting and cast to produce an ingot. The ingot is subjected to surface-milling (a surface-smoothening treatment) and a homogenization heat treatment, thereby giving an ingot for a core (a member for a core), an ingot for a sacrificial material, and an ingot for a brazing filler metal. Then, the ingot for a sacrificial material and the ingot for a brazing filler metal are each hot-rolled to a predetermined thickness, thereby giving a member for a sacrificial material and a member for a brazing filler metal. Next, the member for a sacrificial material is laminated on one side of the member for a core, while the member for a brazing filler metal is laminated on the other side. The laminate is heat-treated (reheated) and then subjected to pressure bonding by hot rolling, thereby giving a plate material. Subsequently, cold rolling and intermediate annealing (continuous annealing) are performed, and further finish cold rolling is performed. Subsequently, finish annealing is performed. Alternatively, after the plate material is formed, only cold rolling is performed without performing intermediate annealing, and then finish annealing is performed. 
     Here, in order for the brazing sheet to have a work hardening exponent n of not less than 0.05 as mentioned above, it is necessary to control the finish cold rolling reduction and the finish annealing conditions in the production process. The conditions are different depending on whether intermediate annealing is performed. Hereinafter, the conditions will be described. 
     &lt;With Intermediate Annealing&gt; 
     In the case where intermediate annealing is performed during cold rolling, a continuous annealing furnace (CAL) is used, and the temperature (maximum attained temperature) is set at 350 to 550° C. When the maximum attained temperature during intermediate annealing is less than 350° C., the solution treatment is insufficient. Accordingly, even when the subsequent finish cold working and finish annealing temperature are controlled, an excessive amount of strain is introduced, which is likely to cause erosion during brazing, resulting in a decrease in erosion resistance. Meanwhile, in order to suppress the melting of the brazing filler metal during annealing, the upper limit of the temperature is not more than 550° C. Incidentally, in intermediate annealing using a continuous annealing furnace, the retention time at a temperature within a range of 350 to 550° C. is not particularly limited, but should usually be not more than 5 minutes (including “no retention”). 
     The finish cold rolling reduction after intermediate annealing should be not less than 55% and preferably not more than 90%. The strain introduced by finish cold rolling affects the softening behavior of the subsequent finish annealing, and, depending on the finish cold rolling reduction and the finish annealing conditions, it is difficult to obtain a work hardening exponent n of not less than 0.05. When the finish cold rolling reduction is less than 55%, the amount of introduced strain is small, thereby the work hardening exponent n becoming smaller than 0.05. Meanwhile, when it is more than 90%, an excessive amount of strain is introduced, which is likely to cause erosion during brazing, possibly resulting in a decrease in erosion resistance. 
     The finish annealing temperature after finish cold rolling is more than 250° C. and not more than 400° C. When the finish annealing temperature is not more than 250° C., it is not effective in relaxing the working strain during rolling, and the work hardening exponent n is less than 0.05. When the finish annealing temperature after finish cold rolling is more than 400° C., the thermal refining is for annealed member and thus recrystallized crystal grain of the core during brazing is not coarsened, resulting in that erosion of the core by melted brazing filler is extremely progressed. Incidentally, the heating time in finish annealing is not particularly limited, but it is usually preferable that the time is 1 to 10 hours. When the heating time is less than 1 hour, there is a possibility that the strength of the brazing sheet is not uniform over the entire coil. Meanwhile, when the time is more than 10 hours, the effect of softening annealing is saturated, which only undermines economic efficiency. 
     &lt;Without Intermediate Annealing&gt; 
     In the case where intermediate annealing is omitted, the cold working rate after hot rolling should be not more than 55% and preferably not more than 97%. When the cold rolling ratio is less than 55%, the amount of introduced strain is small, thereby the work hardening exponent n becoming smaller than 0.05. Meanwhile, when it is more than 97%, there is a possibility that the strength of the material is so high that it is difficult to roll the material to the desired thickness. In addition, the finish annealing conditions after finish cold rolling may also be the same as above. The conditions may include heating at a temperature of more than 250° C. and not more than 400° C. preferably for 1 to 10 hours. Incidentally, for the homogenization of the material structure, after hot rolling, it is possible to perform annealing at 350° C. or higher for 1 hour or longer, for example. 
     EXAMPLES 
     Next, the aluminum alloy brazing sheet for heat exchangers according to the present invention will be described in detail by way of a comparison between examples, where the requirements of the present invention are satisfied, and comparative examples, where the requirements of the present invention are not satisfied. 
     First, an aluminum alloy for a core, an aluminum alloy for a sacrificial material, and an aluminum alloy for a brazing filler metal were melted and cast in a usual manner, followed by a homogenization treatment, thereby giving an ingot for a core (a member for a core), an ingot for a sacrificial material, and an ingot for a brazing filler metal. The ingot for a sacrificial material and the ingot for a brazing filler metal were each hot-rolled to a predetermined thickness, thereby giving a member for a sacrificial material and a member for a brazing filler metal. Further, the member for a sacrificial material was laminated on one side of the member for a core, while the member for a brazing filler metal was laminated on the other side, in such a manner that the brazing filler metal clad ratio and the sacrificial material clad ratio were each 15%. The laminate was then subjected to pressure bonding by hot rolling to give a plate material. Subsequently, cold rolling, intermediate annealing (at a predetermined temperature for 1 minute), finish cold rolling, and finish annealing (at a predetermined temperature for 3 hours) were performed, or alternatively cold rolling and finish annealing (at a predetermined temperature for 3 hours) were performed, thereby giving a plate having a thickness of 0.25 mm. 
     The components of the core, the sacrificial material, and the brazing filler metal are shown in Tables 1 to 3. Incidentally, in Tables 1 and 2, components that are not contained are indicated with “-”, and values that do not satisfy the configuration of the present invention are underlined. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Core Composition 
               
            
           
           
               
               
               
            
               
                   
                 % by mass 
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
            
               
                   
                 No. 
                 Si 
                 Cu 
                 Mn 
                 Cr 
                 Ti 
                 Mg 
                 Fe 
                 Remarks 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
            
               
                 Examples 
                 S1 
                 1.00 
                 0.50 
                 1.90 
                 — 
                 — 
                 — 
                 — 
                   
               
               
                   
                 S2 
                 0.90 
                 0.55 
                 1.90 
                 0.15 
                 — 
                 — 
                 — 
               
               
                   
                 S3 
                 0.20 
                 1.00 
                 0.60 
                 0.25 
                 — 
                 — 
                 — 
               
               
                   
                 S4 
                 0.55 
                 1.00 
                 0.60 
                 — 
                 0.05 
                 — 
                 — 
               
               
                   
                 S5 
                 0.65 
                 0.65 
                 1.00 
                 — 
                 0.25 
                 — 
                 — 
               
               
                   
                 S6 
                 0.70 
                 0.70 
                 1.00 
                 0.05 
                 — 
                 0.05 
                 — 
               
               
                   
                 S7 
                 0.25 
                 0.75 
                 2.00 
                 — 
                 — 
                 0.50 
                 — 
               
               
                   
                 S8 
                 0.80 
                 0.65 
                 1.50 
                 — 
                 — 
                 — 
                 0.20 
               
               
                   
                 S9 
                 0.10 
                 1.10 
                 2.00 
                 0.05 
                 — 
                 — 
                 0.15 
               
               
                   
                 S10 
                 0.10 
                 0.90 
                 2.00 
                 0.20 
                 0.10 
                 — 
                 — 
               
               
                   
                 S11 
                 0.25 
                 0.50 
                 0.80 
                 — 
                 0.20 
                 0.25 
                 — 
               
               
                   
                 S12 
                 0.35 
                 0.85 
                 0.80 
                 0.05 
                 0.10 
                 0.15 
                 0.10 
               
               
                 Comparative Examples 
                 S13 
                 
                   0.05 
                 
                 0.70 
                 1.00 
                 — 
                 — 
                 — 
                 — 
                 Too little Si 
               
               
                   
                 S14 
                 
                   1.05 
                 
                 0.50 
                 0.50 
                 — 
                 — 
                 — 
                 — 
                 Too much Si 
               
               
                   
                 S15 
                 0.30 
                 
                   0.45 
                 
                 1.90 
                 0.10 
                 — 
                 — 
                 — 
                 Too little Cu 
               
               
                   
                 S16 
                 0.50 
                 
                   1.25 
                 
                 1.30 
                 — 
                 0.10 
                 — 
                 — 
                 Too much 
               
               
                   
                   
                   
                   
                   
                   
                   
                   
                   
                 Cu 
               
               
                   
                 S17 
                 0.40 
                 0.60 
                 
                   0.45 
                 
                 — 
                 — 
                 0.20 
                 — 
                 Too little Mn 
               
               
                   
                 S18 
                 0.20 
                 1.10 
                 
                   2.05 
                 
                 — 
                 — 
                 — 
                 0.05 
                 Too much 
               
               
                   
                   
                   
                   
                   
                   
                   
                   
                   
                 Mn 
               
               
                   
                 S19 
                 0.80 
                 0.60 
                 1.00 
                 
                   0.30 
                 
                 — 
                 — 
                 0.05 
                 Too much 
               
               
                   
                   
                   
                   
                   
                   
                   
                   
                   
                 Cr 
               
               
                   
                 S20 
                 0.40 
                 0.90 
                 1.40 
                 0.10 
                 
                   0.03 
                 
                 — 
                 — 
                 Too little Ti 
               
               
                   
                 S21 
                 0.20 
                 0.90 
                 0.60 
                 0.20 
                 
                   0.27 
                 
                 — 
                 — 
                 Too much Ti 
               
               
                   
                 S22 
                 0.90 
                 0.70 
                 1.90 
                 — 
                 0.15 
                 
                   0.03 
                 
                 — 
                 Too little Mg 
               
               
                   
                 S23 
                 0.95 
                 0.50 
                 0.55 
                 — 
                 — 
                 
                   0.55 
                 
                 0.15 
                 Too much 
               
               
                   
                   
                   
                   
                   
                   
                   
                   
                   
                 Mg 
               
               
                   
               
               
                 *Balance: Al and unavoidable impurities 
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 Sacrificial Material Composition 
               
            
           
           
               
               
               
            
               
                   
                 % by mass 
                   
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 No. 
                 Si 
                 Zn 
                 Mg 
                 Remarks 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                   
                 Examples 
                 G1 
                 0.30 
                 3.05 
                 2.00 
                   
               
               
                   
                   
                 G2 
                 0.30 
                 5.00 
                 2.00 
               
               
                   
                   
                 G3 
                 0.21 
                 5.00 
                 1.00 
               
               
                   
                   
                 G4 
                 0.21 
                 4.50 
                 1.00 
               
               
                   
                   
                 G5 
                 0.55 
                 2.05 
                 4.50 
               
               
                   
                   
                 G6 
                 0.65 
                 2.50 
                 4.00 
               
               
                   
                   
                 G7 
                 0.80 
                 3.50 
                 3.50 
               
               
                   
                 Comparative 
                 G8 
                 
                   0.15 
                 
                 4.00 
                 2.00 
                 Too little Si 
               
               
                   
                 Examples 
                 G9 
                 
                   0.85 
                 
                 3.05 
                 1.50 
                 Too much Si 
               
               
                   
                   
                 G10 
                 0.50 
                 
                   2.00 
                 
                 2.50 
                 Too little Zn 
               
               
                   
                   
                 G11 
                 0.40 
                 
                   2.00 
                 
                 3.00 
                 Too much 
               
               
                   
                   
                   
                   
                   
                   
                 Zn 
               
               
                   
                   
                 G12 
                 0.80 
                 3.05 
                 
                   0.95 
                 
                 Too little Mg 
               
               
                   
                   
                 G13 
                 0.70 
                 3.05 
                 
                   4.60 
                 
                 Too much 
               
               
                   
                   
                   
                   
                   
                   
                 Mg 
               
               
                   
                   
               
               
                   
                 *Balance: Al and unavoidable impurities 
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 3 
               
             
            
               
                   
               
               
                 Brazing Filler Metal Composition 
               
            
           
           
               
               
               
            
               
                   
                   
                 % by mass 
               
               
                   
                 No. 
                 Si 
               
               
                   
                   
               
            
           
           
               
               
               
            
               
                   
                 R1 
                 7.0 
               
               
                   
                 R2 
                 10.0 
               
               
                   
                 R3 
                 12.0 
               
               
                   
                   
               
               
                   
                 *Balance: Al and unavoidable impurities 
               
            
           
         
       
     
     With respect to the test material thus produced, the work hardening exponent n before electric resistance welding was calculated, and the following tests were performed to evaluate the properties. 
     &lt;Measurement of Work Hardening Exponent n&gt; 
     A test material processed into a test piece JIS No. 5 was subjected to a tensile test, and the work hardening exponent n of the brazing sheet was calculated in accordance with the two-point method of JIS Z 2253 at 2% strain and 6% strain. 
     &lt;Evaluation of High Frequency Welding Properties&gt; 
     Using an ordinary slitter apparatus, the test material was slit into a bar having a width dimension of 35 mm and then wound up in the form of a coil. The bar thus obtained was processed into an electric resistance welded tube using an apparatus for producing an electric resistance welded tube, thereby giving a flat tube having a major-axis size of 16 mm and a minor-axis size of 2 mm. The evaluation of high frequency welding properties was executed as an appearance test where the obtained electric resistance welding tube within its lengthy of 100 m is observed for deterring whether or not an unwelded portion exists. In case where the unwelded portion having the lengthy of not less than 5 mm was not found, the high frequency welding property was rated as excellent (∘) whereas in case where one or more unwelded portions having the lengthy of not less than 5 mm were not found, the high frequency welding property was rated as poor (x). 
     &lt;Evaluation of Strength after Brazing&gt; 
     A test material was brazed using a drop test method (heating at a temperature of 600° C. for 5 minutes in a nitrogen atmosphere having a dew point of −40° C. and an oxygen concentration of not more than 200 ppm) and then processed into a test piece JIS No. 5 (three pieces were produced for each test material). The test pieces were allowed to stand at room temperature (25° C.) for one week and then measured for strength after brazing by a tensile test. When the average strength of the three test pieces after brazing was not less than 170 MPa, strength was rated as excellent (∘). When the average was less than 170 MPa, strength was rated as poor (x). Incidentally, the evaluation of strength after brazing was performed only on test materials rated as excellent (∘) in terms of high frequency welding properties. 
     &lt;Evaluation of Erosion Resistance&gt; 
     Test materials were cold-rolled at working rates of 10% and 20%, respectively, and they were brazed using a drop test method (heating at a temperature of 600° C. for 5 minutes in a nitrogen atmosphere having a dew point of −40° C. and an oxygen concentration of not more than 200 ppm). Subsequently, each test material was cut to 2 cm×2 cm squares and embedded in a resin, followed by polishing the cut section. Subsequently, the polished surface was observed under a microscope. In the case where not less than 60% of the core of each test material was robust, erosion resistance was rated as excellent (∘). In the case where the percentage was less than 60% in one or more of the test materials, erosion resistance was rated as poor (x). Incidentally, the evaluation of erosion resistance was performed only on test materials rated as excellent (∘) in terms of high frequency welding properties and strength after brazing. 
     &lt;Evaluation of Brazeability&gt; 
     A test piece with a size of 25 mm in width×60 mm in length was cut from a test material. To the brazing filler metal surface of the test piece, a non-corrosive flux FL-7 (manufactured by Morita Chemical Industries) was applied in an amount of 5 g/m 2  and dried. As shown in  FIG. 3 , the test piece (lower plate  11 ) was placed in such a manner that the brazing filler metal surface having the flux applied thereto faced up. Using a round bar of φ 2 mm made of stainless steel as a spacer  12  thereon, a 3003 alloy plate (upper plate  13 ) 1 mm in thickness, 25 mm in width, and 55 mm in length was placed perpendicularly to the test piece and fixed with a wire. At this time, the position of the spacer  12  was 50 mm away from one end of the test piece. Brazing was then performed (heating at a temperature of 600° C. for 5 minutes in a nitrogen atmosphere having a dew point of −40° C. and an oxygen concentration of not more than 200 ppm). The length of the fillet filling the gap  14  between the test piece (lower plate  11 ) and the 3003 alloy plate (upper plate  13 ) was measured. When the fillet length was not less than 30 mm, brazeability is rated as excellent (∘). When the fillet length was less than 30 mm, brazeability is rated as poor (x). Incidentally, the evaluation of brazeability was performed only on test materials rated as excellent in terms of all of high frequency welding properties, strength after brazing, and erosion resistance. 
     &lt;Evaluation of Corrosion Resistance&gt; 
     A test material was brazed using a drop test method (heating at a temperature of 600° C. for 5 minutes in a nitrogen atmosphere having a dew point of −40° C. and an oxygen concentration of not more than 200 ppm) and then cut to a size of 50 mm in width×60 mm in length. Further, the brazing filler metal surface was entirely covered with a masking seal with a size of 60 mm in width×70 mm in length. In addition, the seal was folded back to the sacrificial-material-surface side such that the portion 5 mm from each edge of the sacrificial material was also covered with the seal. A test piece was thus produced. 
     The test piece was subjected to a corrosion resistance test including 90 cycles of the following procedure: the specimen is immersed in a test solution containing Na + : 118 ppm, Cl − : 58 ppm, SO 4   2− : 60 ppm, Cu 2+ : 1 ppm, and Fe 3+ : 30 ppm (88° C.×8 hours), then naturally cooled to room temperature, and maintained at room temperature for 16 hours. The corrosion state was visually observed. When the maximum corrosion depth of the test piece was not more than 50 μM, corrosion resistance was rated as excellent (∘). When the maximum corrosion depth was more than 50 μm, corrosion resistance was rated as poor (x). Incidentally, the evaluation of corrosion resistance was performed only on test materials rated as excellent in terms of all of high frequency welding properties, strength after brazing, erosion resistance, and brazeability. 
     The test results are shown in Tables 4 and 5. Incidentally, in Tables 4 and 5, test materials that were unevaluable or were not evaluated are indicated with “-”, and the values of test materials which do not satisfy the configuration of the present invention or whose production conditions do not satisfy the requirements are underlined. 
     
       
         
           
               
               
               
               
               
               
               
               
               
               
               
               
               
             
               
                 TABLE 4 
               
               
                   
               
               
                   
                   
                   
                   
                   
                   
                   
                   
                 High 
                   
                   
                   
                   
               
               
                   
                   
                   
                 Brazing 
                   
                 Finish 
                   
                   
                 Frequency 
                 Strength 
                   
                   
                 Corrosion 
               
               
                   
                 Sacrificial 
                   
                 Filler 
                 Intermediate 
                 Cold 
                 Finish 
                   
                 Welding 
                 after 
                 Erosion 
                   
                 Resistance 
               
               
                 No. 
                 Material 
                 Core 
                 Metal 
                 Annealing 
                 Rolling 
                 Annealing 
                 nValue 
                 Properties 
                 Brazing 
                 Resistance 
                 Brazeability 
                 (Inner Side) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
               
               
            
               
                 1 
                 G1 
                 S1 
                 R1 
                 450 
                 55 
                 400 
                 0.21 
                 ◯ 
                 ◯ 
                 ◯ 
                 ◯ 
                 ◯ 
               
               
                 2 
                 G1 
                 S2 
                 R1 
                 450 
                 55 
                 400 
                 0.21 
                 ◯ 
                 ◯ 
                 ◯ 
                 ◯ 
                 ◯ 
               
               
                 3 
                 G1 
                 S3 
                 R1 
                 450 
                 55 
                 255 
                 0.07 
                 ◯ 
                 ◯ 
                 ◯ 
                 ◯ 
                 ◯ 
               
               
                 4 
                 G1 
                 S4 
                 R1 
                 450 
                 55 
                 255 
                 0.06 
                 ◯ 
                 ◯ 
                 ◯ 
                 ◯ 
                 ◯ 
               
               
                 5 
                 G1 
                 S5 
                 R1 
                 450 
                 90 
                 300 
                 0.11 
                 ◯ 
                 ◯ 
                 ◯ 
                 ◯ 
                 ◯ 
               
               
                 6 
                 G1 
                 S6 
                 R1 
                 450 
                 90 
                 300 
                 0.10 
                 ◯ 
                 ◯ 
                 ◯ 
                 ◯ 
                 ◯ 
               
               
                 7 
                 G1 
                 S7 
                 R1 
                 450 
                 90 
                 300 
                 0.13 
                 ◯ 
                 ◯ 
                 ◯ 
                 ◯ 
                 ◯ 
               
               
                 8 
                 G1 
                 S8 
                 R1 
                 450 
                 90 
                 300 
                 0.12 
                 ◯ 
                 ◯ 
                 ◯ 
                 ◯ 
                 ◯ 
               
               
                 9 
                 G1 
                 S9 
                 R1 
                 450 
                 70 
                 255 
                 0.08 
                 ◯ 
                 ◯ 
                 ◯ 
                 ◯ 
                 ◯ 
               
               
                 10 
                 G1 
                 S10 
                 R1 
                 450 
                 70 
                 255 
                 0.07 
                 ◯ 
                 ◯ 
                 ◯ 
                 ◯ 
                 ◯ 
               
               
                 11 
                 G1 
                 S11 
                 R1 
                 450 
                 70 
                 270 
                 0.08 
                 ◯ 
                 ◯ 
                 ◯ 
                 ◯ 
                 ◯ 
               
               
                 12 
                 G1 
                 S12 
                 R1 
                 450 
                 70 
                 270 
                 0.07 
                 ◯ 
                 ◯ 
                 ◯ 
                 ◯ 
                 ◯ 
               
               
                 13 
                 G1 
                 S1 
                 R1 
                 350 
                 70 
                 270 
                 0.07 
                 ◯ 
                 ◯ 
                 ◯ 
                 ◯ 
                 ◯ 
               
               
                 14 
                 G2 
                 S1 
                 R1 
                 550 
                 70 
                 270 
                 0.10 
                 ◯ 
                 ◯ 
                 ◯ 
                 ◯ 
                 ◯ 
               
               
                 15 
                 G3 
                 S1 
                 R1 
                 Not performed 
                 97 
                 270 
                 0.12 
                 ◯ 
                 ◯ 
                 ◯ 
                 ◯ 
                 ◯ 
               
               
                 16 
                 G4 
                 S1 
                 R1 
                 Not performed 
                 97 
                 270 
                 0.13 
                 ◯ 
                 ◯ 
                 ◯ 
                 ◯ 
                 ◯ 
               
               
                 17 
                 G5 
                 S1 
                 R1 
                 Not performed 
                 70 
                 300 
                 0.16 
                 ◯ 
                 ◯ 
                 ◯ 
                 ◯ 
                 ◯ 
               
               
                 18 
                 G6 
                 S1 
                 R1 
                 Not performed 
                 70 
                 300 
                 0.15 
                 ◯ 
                 ◯ 
                 ◯ 
                 ◯ 
                 ◯ 
               
               
                 19 
                 G7 
                 S1 
                 R1 
                 Not performed 
                 55 
                 300 
                 0.14 
                 ◯ 
                 ◯ 
                 ◯ 
                 ◯ 
                 ◯ 
               
               
                 20 
                 G1 
                 S1 
                 R1 
                 Not performed 
                 55 
                 300 
                 0.14 
                 ◯ 
                 ◯ 
                 ◯ 
                 ◯ 
                 ◯ 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
               
               
               
               
               
               
               
               
               
               
               
               
             
               
                 TABLE 5 
               
               
                   
               
               
                   
                   
                   
                   
                   
                 Finish 
                   
                   
                   
                   
                   
                   
                   
               
               
                   
                   
                   
                   
                   
                 Cold 
                   
               
               
                   
                   
                   
                   
                   
                 Rolling 
                   
               
               
                   
                   
                   
                   
                 Intermediate 
                 Cold 
                 Finish 
                   
                 High 
               
               
                   
                   
                   
                 Brazing 
                 Annealing 
                 Rolling 
                 Annealing 
                   
                 Frequency 
                   
                   
                   
                 Corrosion 
               
               
                   
                 Sacrificial 
                   
                 Filler 
                 Temperature 
                 Ratio 
                 Temperature 
                   
                 Welding 
                 Strength 
                 Erosion 
                   
                 Resistance 
               
               
                 No. 
                 Material 
                 Core 
                 Metal 
                 [° C.] 
                 [%] 
                 [° C.] 
                 nValue 
                 Properties 
                 after Brazing 
                 Resistance 
                 Brazeability 
                 (Inner Side) 
               
               
                   
               
             
            
               
                 21 
                 G1 
                 
                   S13 
                 
                 R1 
                 450 
                 70 
                 300 
                 0.12 
                 ◯ 
                 X 
                 — 
                 — 
                 — 
               
               
                 22 
                 G1 
                 
                   S14 
                 
                 R1 
                 450 
                 70 
                 300 
                 0.13 
                 ◯ 
                 — 
                 — 
                 — 
                 — 
               
               
                 23 
                 G1 
                 
                   S15 
                 
                 R1 
                 450 
                 70 
                 300 
                 0.12 
                 ◯ 
                 X 
                 — 
                 — 
                 — 
               
               
                 24 
                 G1 
                 
                   S16 
                 
                 R1 
                 450 
                 70 
                 300 
                 0.11 
                 ◯ 
                 — 
                 — 
                 — 
                 — 
               
               
                 25 
                 G1 
                 
                   S17 
                 
                 R1 
                 450 
                 7 
                 300 
                 0.11 
                 ◯ 
                 — 
                 — 
                 — 
                 — 
               
               
                 26 
                 G1 
                 
                   S18 
                 
                 R1 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 27 
                 G1 
                 
                   S19 
                 
                 R1 
                 450 
                 70 
                 300 
                 0.13 
                 ◯ 
                 ◯ 
                 ◯ 
                 ◯ 
                 X 
               
               
                 28 
                 G1 
                 
                   S20 
                 
                 R1 
                 450 
                 70 
                 300 
                 0.12 
                 ◯ 
                 ◯ 
                 ◯ 
                 ◯ 
                 X 
               
               
                 29 
                 G1 
                 
                   S21 
                 
                 R1 
                 450 
                 70 
                 300 
                 0.13 
                 ◯ 
                 ◯ 
                 ◯ 
                 ◯ 
                 X 
               
               
                 30 
                 G1 
                 
                   S22 
                 
                 R1 
                 450 
                 70 
                 300 
                 0.12 
                 ◯ 
                 X 
                 — 
                 — 
                 — 
               
               
                 31 
                 G1 
                 
                   S23 
                 
                 R1 
                 450 
                 70 
                 270 
                 0.08 
                   
                 ◯ 
                 ◯ 
                 X 
                 — 
               
               
                 32 
                 
                   G8 
                 
                 S1 
                 R1 
                 450 
                 70 
                 270 
                 0.07 
                 ◯ 
                 X 
                 — 
                 — 
                 — 
               
               
                 33 
                 
                   G9 
                 
                 S1 
                 R1 
                 450 
                 70 
                 270 
                 0.07 
                 ◯ 
                 — 
                 — 
                 — 
                 — 
               
               
                 34 
                 
                   G10 
                 
                 S1 
                 R1 
                 450 
                 70 
                 270 
                 0.10 
                 ◯ 
                 ◯ 
                 ◯ 
                 ◯ 
                 X 
               
               
                 35 
                 
                   G11 
                 
                 S1 
                 R1 
                 450 
                 70 
                  27 
                 0.08 
                 ◯ 
                 — 
                 — 
                 — 
                 — 
               
               
                 36 
                 
                   G12 
                 
                 S1 
                 R2 
                 450 
                 85 
                 300 
                 0.09 
                 X 
                 X 
                 — 
                 — 
                 — 
               
               
                 37 
                 
                   G13 
                 
                 S1 
                 R3 
                 — 
                 — 
                 — 
                 — 
                   
                 — 
                 — 
                 — 
                 — 
               
               
                 38 
                 G1 
                 S1 
                 R1 
                 
                   560 
                 
                 — 
                 — 
                 — 
                   
                 — 
                 — 
                 — 
                 — 
               
               
                 39 
                 G1 
                 S1 
                 R1 
                 450 
                 
                   50 
                 
                 270 
                 
                   0.04 
                 
                   
                 — 
                 — 
                 — 
                 — 
               
               
                 40 
                 G1 
                 S1 
                 R1 
                 Not 
                 
                   50 
                 
                  27 
                 
                   0.04 
                 
                   
                 — 
                 — 
                 — 
                 — 
               
               
                   
                   
                   
                   
                 performed 
               
               
                 41 
                 G1 
                 S1 
                 R1 
                 450 
                 70 
                 
                   245 
                 
                 
                   0.03 
                 
                   
                 — 
                 — 
                 — 
               
               
                   
               
            
           
         
       
     
     As shown in Table 4, test materials Nos. 1 to 20 satisfy the requirements of the present invention and thus were excellent for all the evaluation criteria. 
     Meanwhile, as shown in Table 5, Nos. 21 to 42 do not satisfy the configuration of the present invention, so the results were as follows. 
     In No. 21, the Si content of the core was too low, and thus the strength after brazing was poor. In No. 22, the Si content of the core was too high, and thus the core melted during heating for brazing. In No. 23, the Cu content of the core was too low, and thus the strength after brazing was poor. In No. 24, the Cu content of the core was too high, and thus the core melted during heating for brazing. 
     In No. 25, the Mn content of the core was too low, and thus the strength after brazing was poor. In No. 26, the Mn content of the core was too high, and thus rolling was not possible, making it impossible to produce a brazing sheet. In No. 27, the Cr content of the core was too high, and thus the corrosion resistance was poor. In No. 28, the Ti content of the core was too low, and thus the corrosion resistance was poor. In No. 29, the Ti content of the core was too high, and thus the corrosion resistance was poor. In No. 30, the Mg content of the core was too low, and thus the strength after brazing was poor. In No. 31, the Mg content of the core was too high, and thus the brazeability was poor. 
     In No. 32, the Si content of the sacrificial material was too low, and thus the strength after brazing was poor. In No. 33, the Si content of the sacrificial material was too high, and thus the sacrificial material melted during heating for brazing. In No. 34, the Zn content of the sacrificial material was too low, and thus the corrosion resistance was poor. In No. 35, the Zn content of the sacrificial material was too high, and thus the sacrificial material melted during heating for brazing. 
     In No. 36, the Mg content of the sacrificial material was too low, and thus the strength after brazing was poor. In No. 37, the Mg content of the sacrificial material was too high, and thus rolling was not possible, making it impossible to produce a brazing sheet. In No. 38, the temperature of intermediate annealing was high, and thus the brazing filler metal melted, making it impossible to produce a brazing sheet. In Nos. 39 and 40, the cold rolling ratio in finish cold rolling was low, and the n value is too low; as a result, the cracking resistance was poor, leading to poor high frequency welding properties. In No. 41, the temperature of finish annealing was low, and the n value was too small; as a result, the high frequency welding properties were poor. 
     Incidentally, the test material No. 40 assumes the brazing sheet of the prior technique described in JP-A-2001-170793 mentioned above. As this example shows, the brazing sheet of the prior technique does not satisfy the certain level in the above evaluations. Therefore, examples of the present invention objectively show that a brazing sheet according to the present invention is more excellent than a brazing sheet of the prior technique. 
     The present invention has been described in detail with reference to embodiments and examples. However, the gist of the present invention is not limited by the above descriptions, and the scope of the invention is to be understood based on the descriptions of the claims. Incidentally, needless to say, the present invention can be modified or varied, for example, based on the above descriptions.