Aluminum Alloy Processing Method and Aluminum Alloy Workpiece

Abstract

Provided is a method for processing art aluminum alloy comprising: 0.5% by mass or more and 1.0% by mass or less of Mg, 0.5% by mass or more and 3.0% by mass or less of Si, 0.2% by mass or more and 0.4% by mass or less of Cu, 0.15% by mass or more and 0.25% by mass or less of Mn, 0.1% by mass or more and 0.2% by mass or less of Ti, and 120 ppm by mass or less of Sr, the method comprising casting the aluminum alloy and forging the cast aluminum at; a temperature of 200° C. or more and 470° C. or less.

Claims

1. A method for processing an aluminum alloy comprising: 0.5% by mass or more and 1.0% by mass or less of Mg, 0.5% by mass or more and 3.0% by mass or less of Si, 0.2% by mass or more and 0.4% by mass or less of Cu, 0.15% by mass or more and 0.25% by mass or less of Mn, 0.1% by mass or more and 0.2% by mass or less of Ti, and 120 ppm by mass or less of Sr, the method comprising casting the aluminum alloy and forging the cast aluminum at a temperature of 200° C. or more and 470° C. or less.

2. The method for processing the aluminum alloy according to claim 1, wherein the cast aluminum alloy is forged at a temperature of 400° C. or more and 450° C. or less.

3. An aluminum alloy workpiece, comprising: 0.5% by mass or more and 1.0% by mass or less of Mg, 0.5% by mass or more and 3.0% by mass or less of Si, 0.2% by mass or more and 0.4% by mass or less of Cu, 0.15% by mass or more and 0.25% by mass or less of Mn, 0.1% by mass or more and 0.2% by mass or less of Ti, and 120 ppm by mass or less of Sr, and having a Z parameter of 1.44×10.sup.9 s.sup.−1 or more and 1.18×10.sup.15 s.sup.−1 or less.

4. The aluminum alloy workpiece according to claim 3, wherein the aluminum alloy workpiece has a Z parameter of 2.73×10.sup.9 s.sup.−1 or more and 1.58×10.sup.10 s.sup.−1 or less.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] FIG. 1 is a photograph of the aluminum alloy workpiece of Example 1;

[0014] FIG. 2 presents diagrams of crystal orientation maps of three test pieces from each of the aluminum alloy workpieces of Examples 1 and 2 and Comparative Example 1;

[0015] FIG. 3 is a diagram showing relationships between Z parameters and area average crystal grain sizes of the three test pieces from each of the aluminum alloy workpieces of Examples 1 and 2 and Comparative Example 1; and

[0016] FIG. 4 is a diagram showing a relationship between forging temperatures and variations in the area average crystal grain sizes, with respect to the three test pieces from each of the aluminum alloy workpieces of Examples 1 and 2 and Comparative Example 1.

DETAILED DESCRIPTION OF THE INVENTION

Processing Method of Aluminum Alloy

[0017] The processing method of an aluminum alloy of the present embodiment is a method of processing an aluminum alloy containing 0.5% by mass or more and 1.0% by mass or less of Mg, 0.5% by mass or more and 3.0% by mass or less of Si, 0.2% by mass or more and 0.4% by mass or less of Cu, 0.15% by mass or more and 0.25% by mass or less of Mn, 0.1% by mass or more and 0.2% by mass or less of Ti, and 120 ppm by mass or less of Sr.

[0018] The processing method of the aluminum alloy of the present embodiment Includes casting an aluminum alloy, and forging the cast aluminum alloy at a temperature of 200° C. or more and 470° C. or less.

[0019] In the processing method of the aluminum alloy of the present embodiment, an aluminum alloy having a composition as described above is forged at a temperature of 200° C. or more and 470° C. or less, whereby the area average crystal grain sire and variation of area average crystal grain sizes between sites can be reduced. As a result, the aluminum alloy workpiece can be expected to have uniform elongation characteristics, and improved general corrosion resistance and stress corrosion cracking resistance.

[0020] The forging temperature of the aluminum alloy is 200° C. or more and 470° C. or less, and is preferably 400° C. or more and 450° C. or less. When the forging temperature of the aluminum alloy is less than 200° C., hot forging of the aluminum alloy is not possible, and when the forging temperature exceeds 470° C., the aluminum alloy workpiece has a larger area average crystal grain size and a larger variation in the area average crystal grain sizes between sites.

[0021] The content of Mg in the aluminum alloy is 0.5% by mass or more and 1.0% by mass or less, and is preferably 0.5% by mass or more and 0.8% by mass or less.

[0022] The content of Si in the aluminum alloy is 0.5% by mass or more and 3.0% by mass or less, and is preferably 1.5% by mass or more and 2.5% by mass or less.

[0023] The content of Cu in the aluminum alloy is 0.2% by mass or more and 0.4% by mass or less, and is preferably 0.2% by mass or more and 0.3% by mass or less.

[0024] The content of Mn in the aluminum alloy is 0.15% by mass or more and 0.25% by mass or less, and is preferably 0.15% by mass or more and 0.2% by mass or less.

[0025] The content of Ti in the aluminum alloy is 0.1% by mass or more and 0.2% by mass or less, and is preferably 0.15% by mass or more and 0.2% by mass or less.

[0026] The content of Sr in the aluminum alloy is 120 ppm by mass or less, and is preferably 1 ppm by mass or less.

[0027] In addition to the above elements, the aluminum alloy may further contain B or the like.

[0028] The method of casting the aluminum alloy is not particularly limited, and examples thereof include gravity die casting (GDC), low pressure die casting (LPDC), and the like.

[0029] When casting the aluminum alloy, the temperature of a holding furnace which holds molten metal in which the aluminum alloy is molten, is, for example, 700° C. or more and 750° C. or less.

[0030] Further, when casting the aluminum alloy, the temperature of the mold is, for example, 150° C. or more and 200° C. or less.

[0031] When forging an aluminum alloy, the aluminum alloy is heated by using, for example, an electric furnace or the like.

[0032] When forging an aluminum alloy, a mold may be used. At this time, the temperature of the mold is, for example, 150° C. or more and 200° C. or less.

[0033] The processing method of the aluminum alloy of the present embodiment may further include a step of melting the forged aluminum alloy, and a step of artificially aging the aluminum alloy subjected to the melting treatment.

[0034] Conditions for melting the aluminum alloy are, for example, 5.5 hours or more and 6 hours or less at a temperature of 530° C. or more and 540° C. or less. Further, conditions for the artificial aging treatment of the aluminum alloy are, for example, 4 hours or more and 7 hours or less at a temperature of 155° C. or more and 165° C. or less.

Aluminum Alloy Workpiece

[0035] The aluminum alloy workpiece of the present: embodiment is an aluminum alloy workpiece described above, having a Z parameter of 1.44×10.sup.9 s.sup.−1 or more and 1.18×10.sup.15 s.sup.−1 or less. As a result, the aluminum alloy workpiece of the present embodiment has a small area average crystal grain size and a small variation in the area average crystal grain sizes between sites.

[0036] Here, the Z parameter can be obtained by an equation of Zener-Hollomon:

Z=A.Math.ε.Math.exp(Q/RT),

in which A is a material constant, ε is a strain rate, Q is an activation energy, R is the gas constant, and T is an absolute temperature. At this time, ε and T are a strain rate and an absolute temperature, respectively, when forging the aluminum alloy.

[0037] When determining the Z parameter of the aluminum alloy workpiece of the present embodiment, A, Q, and R are set to 1, 142,000 J/mol, and 8.314 J/mol K, respectively.

[0038] The Z parameter of the aluminum alloy workpiece of the present embodiment is 1.44×10.sup.9 s.sup.−1 or more and 1.18×10.sup.15 s.sup.−1 or less, and is preferably 2.73×10.sup.9 s.sup.−1 or more and 1.58×10.sup.10 s.sup.−1 or less.

[0039] The area average crystal grain size of the aluminum alloy workpiece of the present embodiment is preferably 300 μm or less.

[0040] The area average crystal grain size of the aluminum alloy workpiece of the present embodiment is usually 150 μm or more.

EXAMPLES

[0041] Hereinafter, the Examples of the present invention will be described, but the present invention is not limited to the Examples.

Example 1

Melting

[0042] An aluminum alloy ingot consisting of Mg (0.6% by mass). Si (1.8% by mass), Cu (0.2% by mass), Mn (0.15% by mass), Ti (0.17% by mass), Sr (1 ppm by mass or less), and Al (balance) was melted using a melting furnace, to obtain a molten metal. At this time, the quality of the aluminum alloy ingot was measured using an inclusion analyzer, PoDFA (manufactured by Pyrotek Co., Ltd.), and it was confirmed that the impurity amount was 0.2 mm.sup.2/kg or less. Furthermore, because an effective addition amount of Mg varies with holding time in the melting furnace, deviation from a component target value was confirmed, using optical emission spectroscopy, and a Mg mother alloy was added to the molten metal to carry out component adjustment before casting. Furthermore, to improve the quality of the molten metal, degassing and fluxing with N.sub.2 gas were performed.

Casting

[0043] The molten metal was conveyed into a holding furnace at 700° C., was poured into a mold in a state of being heated to 200° C., and was cast by GDC to obtain an intermediate. At this time, casting was performed so as to realize directional solidification by cooling the mold with water until solidification of the molten metal was completed. Furthermore, burrs generated during casting were removed using a trimming device, to obtain an intermediate.

Forging

[0044] The intermediate was heated using an electric furnace until it reached 400° C. (forging temperature). At this time, after confirming with a thermocouple that the temperature of the surface of the intermediate reached 400° C., heating was continued for about 30 minutes so that a uniform temperature would be obtained even in the inner part of the intermediate. Next, after confirming that the temperature of the mold reached 200° C., the intermediate was taken out from the electric furnace, and the intermediate was forged using a forging machine.

Heat Treatment

[0045] The intermediate after forging was subjected to a melting treatment and an artificial aging treatment to obtain an aluminum alloy workpiece. The conditions in the melting treatment were 6 hours at 540° C., and the conditions in the artificial aging treatment were 6.5 hours at 160° C.

Example 2

[0046] The same procedures were performed as in Example 1 to obtain an aluminum alloy workpiece, except that the forging temperature was changed to 470° C.

Comparative Example 1

[0047] The same procedures were performed as in Example 1, to obtain an aluminum alloy workpiece, except that the forging temperature was changed to 525° C.

[0048] FIG. 1 is a photograph showing the aluminum alloy workpiece of Example 1. Incidentally, A, B and C in FIG. 1 indicate sites from which the test pieces were cut out when measuring the area crystal grain sizes of aluminum alloy workpieces to be described below.

Crystal Grain Sizes of Aluminum Alloy Workpieces

[0049] Three test pieces were cut. out from sites A, B, and C of each of the aluminum alloy workpieces (see FIG. 1). Next, the test pieces were polished to about #2000 of polishing paper, and then were subjected to final polishing using colloidal silica and ion milling. Then, each of the test pieces was set in a scanning electron microscope (SEM), and an area average crystal grain size of the test piece was measured using electron backscatter diffraction (EBSD). At this time, the grain size and area were acquired by setting a crystal misorientation of 15° or more as a crystal grain boundary.

[0050] Here, if a simple average crystal grain size is used, difference between an apparent crystal grain size and the average crystal grain size is increased, in a case in which a large number of crystal grains, each having a small area, are contained in a structure in which variation exists in the crystal grain sizes. Therefore, an area average crystal grain size d.sub.ave was calculated using the following formula:

d.sub.ave=Σ.sub.id.sub.iA.sub.i/Σ.sub.iA.sub.i   [Equation 1]

in which d.sub.i is an elliptically approximated grain size of the i.sup.th grain and A.sub.i is an area of the i.sup.th grain. Furthermore, difference between the maximum value and the minimum value of the area average crystal grain sizes of the three test pieces was obtained, and the difference was used as the variation of the area average crystal, grain sizes.

[0051] FIG. 2 indicates crystal orientation maps of the three test pieces from each of the aluminum alloy workpieces of Examples 1 and 2 and Comparative Example 1.

[0052] Table 1 shows the area average crystal grain sizes of the three test pieces from each of the aluminum alloy workpieces of Examples 1 and 2 and Comparative Example 1.

TABLE-US-00001 TABLE 1 Area average grain size (μm) Z parameter (s.sup.−1) Site A B C A B C Example 1 133 120 124 .sup. 1.58 × 10.sup.10 .sup. 2.58 × 10.sup.10 .sup. 1.98 × 10.sup.10 Example 2 260 151 188 1.44 × 10.sup.9 2.36 × 10.sup.9 1.81 × 10.sup.9 Comparative Example 1 354 775 390 2.96 × 10.sup.8 4.83 × 10.sup.8 3.71 × 10.sup.8

[0053] FIG. 3 indicates relationships between Z parameters and area average crystal grain sizes of the three test pieces from each of the aluminum alloy workpieces of Examples 1 and 2 and Comparative Example 1.

[0054] From FIG. 3, it can be seen that the aluminum alloy workpieces of Examples 1 and 2 had smaller area average crystal grain sizes than the aluminum alloy workpiece of Comparative Example 1.

[0055] FIG. 4 indicates a relationship between the forging temperatures and the variations in the area average crystal grain sizes, with respect to the three test pieces from each of the aluminum alloy workpieces of Examples 1 and 2 and Comparative Example 1.

[0056] From FIG. 4, it can be seen that the aluminum alloy workpieces of Examples 1 and 2 had smaller variations in the area average crystal grain sizes than the aluminum alloy workpiece of Comparative Example 1. Furthermore, it can be seen from FIG. 4 that the variation in the area average crystal grain sizes at 450° C. was about half the variation in the area average crystal grain sizes at 470° C.