Aluminum Alloy Processing Method and Aluminum Alloy Workpiece

Info

Publication number: 20220298608
Type: Application
Filed: Feb 7, 2022
Publication Date: Sep 22, 2022
Inventors: Satomi MANO (Tokyo), Ayaka YAMAGUCHI (Tokyo)
Application Number: 17/666,503

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.

Description

Description

This application is based on and claims the benefit of priority from Japanese Patent Application No. 2021-042211, filed on 16 Mar. 2021, the content of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a method for processing an aluminum alloy and an aluminum alloy workpiece.

Related Art

As a processing method of a low silicon aluminum alloy, for example, a method in which a low silicon aluminum alloy is subjected to casting, followed by hot forging is known.

As a method for obtaining a part. Patent Document 1 discloses a method including: casting an alloy in a mold; after the casting, demolding the part constituting a preform that is still hot; cooling the preform and then subjecting it to an operation suitable for reheating it to a temperature range of from 470° C. to 550° C.; positioning the part between two shells of a die that defines a cavity of dimensions substantially equal to but less than the dimensions of the cavity of the mold; and strongly pressing the two shells together to exert on the part disposed between said shells a combined effect of pressing and surface kneading. Herein, the low silicon aluminum alloy contains silicon at a content between 0.5% and 3%, magnesium at a content between 0.65% and 1%, copper at a content between 0.20% and 0.40%, manganese at a content between 0.15% and 0.25%, titanium at a content between 0.10% and 0.20%, and strontium at a content between 0 ppm and 120 ppm.

Patent Document 1: Japanese Unexamined Patent Application (Translation of PCT Application), Publication No. 2018-507324

SUMMARY OF THE INVENTION

However, there has been a problem that an area average crystal grain size of an aluminum alloy workpiece increases to about 800 μm, and variation in the area average crystal grain sizes between sites increases.

An object of the present invention is to provide a method for processing an aluminum alloy, the method being able to reduce an area average crystal grain size and a variation in the area average crystal grain sizes between sites, and to provide an aluminum alloy workpiece.

An aspect of the present invention relates to a method for 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, and the method includes casting the aluminum alloy and forging the cast aluminum at a temperature of 200° C. or more and 470° C. or less.

The cast aluminum alloy may be forged at a temperature of 400° C. or more and 450° C. or less.

Another aspect of the present invention relates to an aluminum alloy workpiece 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, and having a Z parameter of 1.44×10⁹s⁻¹or more and 1.18×10¹⁵s⁻¹or less.

The aluminum alloy workpiece may have a Z parameter of 2.73×10⁹s⁻¹or more and 1.58×10¹⁰s⁻¹or less.

According to the present invention, it is possible to provide a processing method which is capable of reducing an area average crystal grain size and a variation in area average crystal grain sizes between sites, and to provide an aluminum alloy workpiece.

BRIEF DESCRIPTION OF THE DRAWINGS

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

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;

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

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

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.

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.

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.

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.

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.

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.

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.

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.

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.

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

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

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.

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.

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

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

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.

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.

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

The aluminum alloy workpiece of the present: embodiment is an aluminum alloy workpiece described above, having a Z parameter of 1.44×10⁹s⁻¹or more and 1.18×10¹⁵s⁻¹or 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.

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

Z=A·ε·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.

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.

The Z parameter of the aluminum alloy workpiece of the present embodiment is 1.44×10⁹s⁻¹or more and 1.18×10¹⁵s⁻¹or less, and is preferably 2.73×10⁹s⁻¹or more and 1.58×10¹⁰s⁻¹or less.

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

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

EXAMPLES

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

Example 1 Melting

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 mm²/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 N₂gas were performed.

Casting

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

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

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

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

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.

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

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.

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_avewas calculated using the following formula:

d_ave=Σ_id_iA_i/Σ_iA_i [Equation 1]

in which d_iis an elliptically approximated grain size of the i^thgrain and A_iis an area of the i^thgrain. 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.

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.

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 1 Area average grain size (μm) Z parameter (s⁻¹) Site A B C A B C Example 1 133 120 124 1.58 × 10¹⁰ 2.58 × 10¹⁰ 1.98 × 10¹⁰ Example 2 260 151 188 1.44 × 10⁹ 2.36 × 10⁹ 1.81 × 10⁹ Comparative Example 1 354 775 390 2.96 × 10⁸ 4.83 × 10⁸ 3.71 × 10⁸

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.

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.

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.

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.

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 1.44×109 s−1 or more and 1.18×1015 s−1 or less.

4. The aluminum alloy workpiece according to claim 3, wherein the aluminum alloy workpiece has a Z parameter of 2.73×109 s−1 or more and 1.58×1010 s−1 or less.