Abstract:
A building structural material produced by A magnesium alloy contains aluminum in a range of 0.1 wt % to 1.0 wt %, zinc in a range of 0.1 wt % to 2.0 wt %, manganese in a range of 0.1 wt % to 1.0 wt %, 0.04 wt % or less copper, 0.05 wt % or less silicon, 0.005 wt % or less iron, and 0.005 wt % or less nickel. This building structural material had no cracks even when it was extruded at an extrusion speed about ten times as high as the conventional speed and also no ignition attributable to surface oxidation occurred.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a malleable magnesium alloy, for example, to such an alloy material subjected to flattening such as extrusion or rolling and a structural material for buildings obtained by flattening the alloy material.  
           [0003]    2. Description of the Related Art  
           [0004]    The term “flattening” mentioned herein denotes a process of subjecting a material to pressure or hammering, such as extrusion molding, rolling, press molding or forging, to work the material into a predetermined shape.  
           [0005]    Malleable magnesium alloys conventionally used for building structural materials include M1, which is an aluminum-zinc alloy prescribed by JIS (Japanese Industrial Standard). The M1 alloy contains, besides magnesium, 3.0% by weight of aluminum and 1.0% by weight of zinc.  
           [0006]    In the case of the conventional malleable magnesium alloy, however, cracking can occur if the extrusion molding speed is increased, making the molding itself impossible. Also, the resulting molded article often oxidizes at its surface and, in some cases, catches fire, so that the surface properties are deteriorated.  
           [0007]    On the other hand, there has been a demand for a magnesium alloy that can be extruded at an increased molding speed.  
         SUMMARY OF THE INVENTION  
         [0008]    The present invention was created in view of the above circumstances, and an object thereof is to provide a malleable magnesium alloy which can be extruded at a higher molding speed than in the case of conventional magnesium alloys and which has satisfactory mechanical properties and corrosion resistance suitable for use as structural materials.  
           [0009]    To achieve the object, the present invention provides a magnesium alloy containing aluminum in a range of 0.1 wt % to 1.0 wt %, zinc in a range of 0.1 wt % to 2.0 wt %, manganese in a range of 0.1 wt % to 1.0 wt %, 0.04 wt % or less copper, 0.05 wt % or less silicon, 0.005 wt % or less iron, and 0.005 wt % or less nickel.  
           [0010]    A billet of the malleable magnesium alloy according to the present invention was actually subjected to extrusion molding. The molded article obtained had no cracks even when it was extruded at an extrusion speed about ten times as high as the conventional speed and also no ignition attributable to surface oxidation occurred. Thus, a structural material of the magnesium alloy could be extrusion molded at a higher extrusion speed than the conventional speed.  
           [0011]    Also, the extrusion molded article produced using the malleable magnesium alloy of the present invention is superior to conventional molded articles in physical properties, such as tensile strength, yield strength, elongation percentage and corrosion resistance, as well as in mechanical properties as a lightweight material.  
           [0012]    The aluminum content is set to fall within the range of 0.1 wt % to 1.0 wt % for the following reasons: If the aluminum content is lower than 0.1 wt %, the resulting molded article fails to show satisfactory mechanical properties as a structural material, and if the aluminum content is higher than 1.0 wt %, it is difficult to extrude the alloy at a higher extrusion speed than the conventional speed.  
           [0013]    Zinc is contained in the range of 0.1 wt % to 2.0 wt %, because if the zinc content is lower than 0.1 wt %, the corrosion resistance lowers, and if the zinc content is higher than 2.0 wt %, it is difficult to extrude the alloy at a higher extrusion speed than the conventional speed.  
           [0014]    Also, manganese is contained in the range of 0.1 wt % to 1.0 wt %, because manganese contained in this range serves to enhance the corrosion resistance. If the manganese content is lower than 0.1 wt %, the corrosion resistance greatly lowers, and if the manganese content is higher than 1.0 wt %, it is difficult to extrude the alloy at a higher extrusion speed than the conventional speed.  
           [0015]    Preferably, the malleable magnesium alloy according to the present invention contains aluminum in a range of 0.2 wt % to 0.8 wt %, zinc in a range of 0.2 wt % to 1.0 wt %, 0.3 wt % manganese, copper in a range of 0.02 wt % to 0.04 wt %, silicon in a range of 0.02 wt % to 0.03 wt %, 0.004 wt % iron, and 0.001 wt % nickel, the balance being magnesium.  
           [0016]    These elements are contained in the respective ranges mentioned, because as a result of experiments, it was found that the extrusion speed could be increased to a level about ten times as high as the conventional speed and that the resulting extrusion molded article was superior to conventional molded articles in mechanical properties such as tensile strength.  
           [0017]    Copper, silicon, iron and nickel are unavoidable impurity elements.  
           [0018]    Calcium may further be added to enhance flame retardancy. In this case, calcium is preferably added in a range of 0.3 to 1.0 wt %.  
           [0019]    Also, rare earth elements such as yttrium, neodymium and cerium may be added each in an amount of 100 ppm or less by weight, in order to improve the mechanical properties at high temperatures. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0020]    [0020]FIG. 1 is a sectional view of an extrusion molded shape; and  
         [0021]    [0021]FIG. 2 is a sectional view of another extrusion molded shape with a sectional form different from that shown in FIG. 1. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
     Examples  
       [0022]    As Examples 1 to 3, billets of malleable magnesium alloy were prepared which contained aluminum, zinc, manganese, silicon, iron, copper and nickel in respective amounts shown in Table 1 below, the balance (Bal.) being magnesium. The figures shown in Table 1 are in the unit wt %.  
       Comparative Examples  
       [0023]    Also, billets having the respective compositions shown in Table 1 were prepared as Comparative Examples 1 to 3.  
                                                                                         TABLE 1                                   Al   Zn   Mn   Si   Fe   Cu   Ni   Mg                                    Example 1   0.5   0.25   0.3   0.03   0.004   0.03   0.001   Bal.       Example 2   0.8   0.2   0.3   0.02   0.004   0.02   0.001   Bal.       Example 3   0.2   1.0   0.3   0.03   0.004   0.04   0.001   Bal.       Comparative   3.0   1.0   0.3   0.02   0.005   0.04   0.002   Bal.       Example 1       Comparative   0.8   2.5   0.3   0.03   0.004   0.03   0.001   Bal.       Example 2       Comparative   0.8   0.5   1.2   0.03   0.004   0.03   0.001   Bal.       Example 3                  
 
         [0024]    The billets of Examples 1 to 3 and Comparative Examples 1 to 3 were each extrusion molded into a shape having a sectional form shown in FIG. 1. For experimental purposes, the extrusion molding was performed at different extrusion speeds, that is, at 5 m/min., 10 m/min., 15 m/min., 30 m/min., 50 m/min. and 70 m/min. The results are shown in Table 2 below. The dimensions of the shape shown in FIG. 1 were: W=50 mm, S=15 mm, and t (thickness)=1.2 mm. The extrusion conditions for the individual examples and comparative examples were as follows: billet temperature=400° C., and extrusion load=3 to 5 MN (meganewtons).  
                                                                                   TABLE 2                                       Extrusion speed (m/min.)                5   10   15   30   50   70                        Example 1   ◯   ◯   ◯   ◯   ◯   ◯       Example 2   ◯   ◯   ◯   ◯   ◯   x       Example 3   ◯   ◯   ◯   ◯   ◯   x       Comparative   ◯   x   x   —   —   —       Example 1       Comparative   ◯   x   x   —   —   —       Example 2       Comparative   ◯   x   x   —   —   —       Example 3                  
 
         [0025]    In Table 2, the mark “ο” indicates that the extrusion molding could be carried out satisfactorily, “x” indicates that the surface properties deteriorated due to cracks, and “−” indicates that the extrusion molding failed because of cracks.  
         [0026]    Also, the billets of Example 1 and Comparative Example 1 were each extrusion molded into a shape having a sectional form shown in FIG. 2. The results are shown in Table 3 below. The dimensions of the shape shown in FIG. 2 were: W=40 mm, S=20 mm, V=15 mm, and t (thickness)=2.0 mm. The other conditions were identical with those for the extrusion molded articles shown in Table 2. In Table 3, the respective marks have the same meanings as explained above with reference to Table 2.  
                                                                                   TABLE 3                                       Extrusion speed (m/min.)                1   2   5   10   15   20                        Example 1   ◯   ◯   ◯   ◯   ◯   ◯       Comparative   ◯   ◯   x   —   —   —       Example 1                  
 
         [0027]    Further, with respect to the shapes of Examples 1 to 3 and Comparative Examples 1 to 3 extrusion molded at the respective extrusion speeds shown in Table 2, the tensile strength was measured, the results being shown in Table 4 below. The tensile strength was measured with a universal testing machine. The numbers shown in Table 4 are in the unit MPa (megapascals). In Table 4, Comparative Examples 1 to 3 extrusion molded at an extrusion speed of 10 m/min. had poor surface properties as indicated by the mark “x” in Table 2, but their tensile strengths were measured for the sake of comparison.  
                                                                           TABLE 4                                       Extrusion speed (m/min.)                    5   10   30   70                            Example 1   240   240   240   240           Example 2   250   250   250   240           Example 3   240   240   240   230           Comparative   280   200   not   not           Example 1           extrudable   extrudable           Comparative   260   180   not   not           Example 2           extrudable   extrudable           Comparative   270   200   not   not           Example 3           extrudable   extrudable                      
 
         [0028]    As is clear from Table 2, Examples 1 to 3 could be extruded satisfactorily at each of the extrusion speeds (molding speeds) 5 m/min., 10 m/min., 15 m/min., 30 m/min. and 50 m/min. Also, the external appearance was visually inspected and no deterioration in surface properties was observed. Example 1 in particular could be extruded even at a speed of 70 m/min., without entailing deterioration in surface properties. Comparative Examples 1 to 3, by contrast, could be extruded at a speed of 10 m/min. but their surface properties were deteriorated, and at a speed of 15 m/min. or above, the extrusion molding itself could not be carried out because of cracking. Namely, Examples 1 to 3 could be extrusion molded at an extrusion speed more than ten times as high as that of Comparative Examples 1 to 3.  
         [0029]    With regard to the extrusion molding of shapes having the sectional form shown in FIG. 2, Example 1 could be extruded even at a speed of 20 m/min., as seen from Table 3, but Comparative Example 1 cracked at a speed of 5 m/min. and could not be extruded. Also, as seen from the results shown in Tables 2 and 3, it is apparent that in the case of extrusion molding shapes with an identical sectional form, the examples according to the present invention can be extruded at an increased speed more than ten times as high as that of the comparative examples, though the extrusion speed can vary depending upon the sectional form of shapes to be extruded.  
         [0030]    As regards the tensile strength of the shapes of the examples and the comparative examples, the tensile strengths of Comparative Examples 1 to 3 greatly lowered with increase in the extrusion speed, as seen from Table 4, but in the case of the examples according to the present invention, the shapes extruded at increased speeds showed tensile strengths nearly equal to those of the shapes extruded at low extrusion speeds. Especially, Examples 1 to 3 extruded at the extrusion speed 10 m/min. all had higher tensile strengths than Comparative Examples 1 to 3 extruded at the same speed. A typical tensile strength of A6063 (JIS), which is a malleable aluminum alloy generally used, is 220 MPa, and thus the examples of the present invention are superior to this malleable aluminum alloy in the tensile strength.  
         [0031]    Also, Examples 1 to 3 were measured as to the 0.2%-yield strength and the elongation percentage, and as a result, the examples had a 0.2%-yield strength of 110 to 130 MPa and showed an elongation percentage of 8 to 12%. Further, to measure the corrosion resistance, the examples were sprayed with salt water containing 5% NaCl for 24 hours, and the reduction in weight due to corrosion was found to be 2 mg/cm 2 /day. These values show that the magnesium alloy according to the present invention has mechanical properties equivalent to or superior to those of the malleable aluminum alloy A6063 (JIS) generally used and can be suitably used as a lightweight structural material.  
         [0032]    Further, using billets of Examples 1 to 3 with 0.3 to 1.0 wt % calcium added, shapes were obtained by extrusion molding. The shapes could be extruded at speeds equivalent to those of Examples 1 to 3 and also had equivalent mechanical properties. Compared with the shapes containing no calcium, the shapes admixed with calcium were less liable to ignition attributable to surface oxidation and showed higher flame retardancy.  
         [0033]    Also, using billets of Examples 1 to 3 additionally containing rare earth elements, such as yttrium, neodymium and cerium, each in an amount of 100 ppm or less by weight, shapes were prepared by extrusion molding. The shapes could be extrusion molded at speeds equivalent to those of Examples 1 to 3 and also had mechanical properties superior to those of the examples at high temperatures (200° C. to 300° C.)  
         [0034]    The molding process to be employed for the malleable magnesium alloy according to the present invention is not limited to extrusion molding, and the magnesium alloy may alternatively be subjected to rolling, press molding or forging. Molded articles obtained by such molding processes also have advantages similar to those of the aforementioned extrusion molded articles.  
         [0035]    As described above, the magnesium alloy of the present invention can be extrusion molded at an extrusion speed higher than the conventional speed. In addition, the extrusion molded article is not deteriorated in its surface properties due to cracking or ignition attributable to surface oxidation.