JPH10298723A - Manufacture of aluminum alloy die casting - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide such a product that is sufficient in strength and excellent in corrosion resistance, by die-casting an Al-Si-Cu alloy to which a prescribed quantity of Cu is added, and unifying the Cu concentration in the Al phase through a solution heat treatment at a prescribed temperature. SOLUTION: The die-casting is achieved using the Al-Si-Cu alloy consisting of Al phase, Si phase and Cu phase. The solution heat treatment is executed to the die-casting at a temperature of 360-400 deg.C, and the Cu concentration is unified so that the layer where the Cu concentration is >=2.5 wt.% in the Al phase in contact with the Si phase is <=3 μm in thickness. It is preferable to use ADC 12 having the weight composition where 1.5-2.0% Cu is added as the Al-Si-Cu alloy. Excellent corrosion resistance can be obtained irrespective of the solution heat treatment condition by unifying the Cu concentration. Because the alloy itself in the die-casting of the aluminum alloy is excellent in corrosion resistance, applications of the product without any paining to which the corrosion resistance is strongly requested, can be expanded.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an aluminum alloy die-cast product having excellent corrosion resistance.

[0002]

2. Description of the Related Art When an aluminum alloy casting is manufactured by a die casting method, an Al-Si-Cu alloy (for example, ADC12) is frequently used. Since this alloy contains 1.5 to 4.0% by weight of Cu which lowers the corrosion resistance, there is a disadvantage that the corrosion resistance of the obtained die-cast product is lowered. Therefore, when the Cu content is reduced in order to improve the corrosion resistance, there is a problem that the strength is reduced. In addition, according to the ordinary die casting method in which the molten metal is filled into the mold cavity at high speed and high pressure in the atmosphere, there are many bubbles entrained during casting in the obtained die cast product,
When a normal solution treatment (solution solution temperature: around 500 ° C.) is performed, it expands and a defect called a blister occurs on the surface. Japanese Patent Application Laid-Open No. 56-163246 discloses a method for producing a heat-treated die cast by heating a die-cast product manufactured by an accurate method or a low-speed die-cast method that does not involve air bubbles during casting to 450 to 530 ° C. Such a special die casting method has problems such as an increase in cost.

[0003]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a manufacturing method capable of obtaining an aluminum alloy die-cast product having sufficient strength and excellent corrosion resistance.

[0004]

Means for Solving the Problems The present inventors have proposed Al-S
As a result of intensive studies on the corrosion resistance of the i-Cu alloy, Cu
Even if the amount of addition is the same, the Cu
It has been found that when the concentration is made uniform, the corrosion resistance is improved as compared with as-cast. That is, the present invention relates to Al-Si-Cu
A die-cast product is cast by a simple ordinary die-casting method in which a molten metal made of a system alloy is filled into a mold cavity in the atmosphere at a high speed and a high pressure.
The solution is subjected to a solution treatment at a temperature of 3 to make the Cu concentration of the Al phase uniform (in the Al phase in contact with the Si phase,
The layer having a u concentration of 2.5% by weight or more becomes 3 μm or less), thereby improving the corrosion resistance. In the present invention, Al
-Cu-added amount of 1.5 to 2.0 as a Si-Cu alloy
% ADC12 is preferably used.

[0005] Al-Si-Cu-based alloys usually have an Al phase,
It is composed of a Si phase and a Cu phase. Corrosion A around Si phase
Since it occurs selectively in the 1 phase, the corrosion resistance is determined mainly by the Cu concentration of the Al phase around the Si phase. Die casting is generally used as-cast. In this case, the concentration of Cu in the Al phase is greatly increased around the Si phase due to segregation. On the other hand, according to the present invention, by increasing the uniformity of the Cu concentration of the Al phase, the layer having a Cu concentration of 2.5% by weight or more in the Al phase in contact with the Si phase is reduced to 3 μm or less. Corrosion resistance is improved. The uniformization of the Cu concentration in the Al phase is achieved by a solution treatment. In the case of Al-Si-Cu alloys, the solution treatment is generally performed at a temperature of about 500 ° C. However, in the above-described ordinary die casting method, a large number of bubbles are entrained in the inside during casting. When the temperature is maintained at this temperature, the inside bubbles expand and a defect called blister occurs on the surface. Therefore, if the solution temperature is lowered, blisters do not occur. However, in order to make the Cu concentration uniform, it is necessary that the average concentration of Cu in the Al phase is lower than the solid solubility of Cu at the solution temperature. Since the solid solubility of Cu decreases as the temperature decreases, the average concentration of Cu in the Al phase must be equal to the solid solubility of Cu in order to make the Cu concentration uniform at a solution temperature of 400 ° C. or less at which blisters do not occur. It is necessary to suppress the Cu addition amount to 2.0% by weight or less so as to be lower. On the other hand, in order to obtain sufficient strength, it is necessary that the added amount of Cu is 1.5% by weight or more. It is necessary to set the solution temperature to 360 ° C. or higher in order to make the content uniform within this range.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION An alloy composed of ADC12 with an added amount of Cu of 1.8% by weight was cast in a JIS boat-shaped mold at room temperature in the air. The obtained ingot was heated at 340 ° C.
7 at each of 360 ° C, 380 ° C, 400 ° C, 500 ° C
After performing the solution treatment for a period of time, it was cooled with water, and a test piece was cut out. Specimens were also cut from as-cast ingots for comparison. A salt spray test (JIS Z2371) was performed on these test pieces for 96 hours to evaluate the corrosion resistance.
After dissolving the rust (aluminum hydroxide) generated on the surface with nitric acid, the weight of rust per unit area was calculated by measuring the Al concentration in nitric acid by ICP (plasma emission spectroscopy). The result is shown in FIG. From FIG. 1, it can be seen that the corrosion resistance improves with an increase in the solution heat-up temperature, and that at 360 ° C. or higher, a sufficiently high corrosion resistance is exhibited as compared to as-cast.

[0007] In order to clarify the relationship between the uniformity of the Cu concentration of the Al phase and the corrosion resistance, an as-cast alloy and a solution treatment at 360 ° C, 400 ° C and 500 ° C were performed using the same alloy as described above. The element distribution of the test piece was measured using EPMA. The results are shown in FIGS. In addition, FIG.
3 (b) and FIGS. 3 (a) and 3 (b) show the elemental distributions at the as-cast, solution temperature of 360 ° C., 400 ° C. and 500 ° C., respectively. In the as-cast state, Cu often shows a peak near the peak of Si (FIG. 2A). This indicates that the Cu concentration of the Al phase around the Si phase has increased significantly due to segregation. At a solution temperature of 360 ° C., the width of the Cu peak around the Si phase becomes narrow, and the layer having a Cu concentration of 2.5% by weight or more
μm or less (FIG. 2B). This indicates that the solution treatment increased the uniformity of the Cu concentration in the Al phase, and reduced the portion with a high Cu concentration around the Si phase. At the solution temperature of 400 ° C. and 500 ° C., no clear peak around the Si phase is seen (FIG. 3 (a),
(B)). This is because the Cu concentration becomes more uniform and the Si concentration becomes higher.
This indicates that the portion having a high Cu concentration around the phase has almost disappeared. From this, it can be seen that at a solution temperature of 360 ° C. or more, the layer having a Cu concentration of 2.5% by weight or more becomes 3 μm or less in the Al phase in contact with the Si phase, so that the corrosion resistance is sufficiently improved. It is considered that high corrosion resistance can be obtained regardless of the solution treatment conditions by making the Cu concentration uniform as described above.

[0008]

As described above, since the aluminum alloy die-cast product obtained by the present invention has excellent corrosion resistance itself, it greatly contributes to the expansion of the use of unpainted products which require corrosion resistance.

[Brief description of the drawings]

FIG. 1 is a diagram showing the relationship between solution temperature and corrosion resistance.

FIG. 2 is a view showing an element distribution of a die-cast product.

FIG. 3 is a diagram showing an element distribution of a die-cast product.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Nozomu Kageyama 5200 Sankajiri, Kumagaya-shi, Saitama, Hitachi Metals Co., Ltd.

Claims (2)

[Claims] 1. A die-cast product is cast by a die-casting method using an Al—Si—Cu-based alloy, and the die-cast product is subjected to a solution treatment at a temperature of 360 to 400 ° C. A method for producing an aluminum alloy die-cast product, wherein a layer having a Cu concentration of 2.5% by weight or more is 3 μm or less. 2. An Al—Si—Cu alloy having a Cu content of 1.
2. The method for producing an aluminum alloy die-cast product according to claim 1, wherein the ADC12 has a weight composition of 5 to 2.0%.