JPH08134576A - Aluminum alloy for die casting - Google Patents

Abstract

PURPOSE: To obtain a die casting having high quality without changing dies by metallurgically suppressing cavities. CONSTITUTION: This aluminum alloy for die casting consists of 7.5 to 12wt.% Si, 0.4 to 0.8wt.% Zr, 0.4 to 0.6wt.% Mg or/and 1.5 to 4.0wt.% Cu and the balance Al with inevitable impurities. ZrAl3 which is the nucleus for primary crystal aluminum is formed and solidification is begun uniformly from the die surfaces to the inside of the thickness by adding Zr to the alloy. The solidified aluminum crystals are, therefore, dispersed and the respective aluminum crystal spacings are made into the finally solidified parts, by which the cavities are dispersed.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to improvements in aluminum alloys for die casting.

[0002]

2. Description of the Related Art As a part of weight reduction of automobile parts, a cylinder block is made of aluminum alloy, and a die-casting method having high productivity is used as a casting method therefor. For example, JP-A-58-42748 "Aluminum alloy for die casting" is a technique for improving corrosion resistance by adding 0.1 to 0.4% Zr to an Al-Si alloy, and JP-A-6-145866. The publication "Aluminum alloy for high pressure casting with excellent castability" is Al
-Si-based alloy with Ti of 0.3% or less and 0.001 to 0.
This is a technology that enables high-pressure casting by adding 1% B.

[0003]

SUMMARY OF THE INVENTION In the above, there is a problem of the generation of cast holes. That is, the die casting method has a higher cooling rate than low pressure casting and high pressure casting, and since directional solidification cannot be achieved, molten metal replenishment due to solidification shrinkage of the thick portion cannot be obtained. Further, since the molten aluminum is filled at a high speed when it is filled in the mold, unavoidable air entrainment and gas components from the chip lubricating liquid in the injection sleeve are mixed. In the molten aluminum filled in the mold in this state, cast cavities in which shrinkage cavities and pores are mixed are concentratedly generated in the thickened portion that finally solidifies. Of course, there are measures for providing an air vent mechanism in the mold to remove air, and forcibly cooling the periphery of the thick portion to increase the solidification rate of the molten aluminum. However, since the air vent mechanism and the forced cooling mechanism cannot be applied depending on the shape of the product, the design of the product and the mold structure must be changed. Therefore, if the porosity can be suppressed metallurgically, a high quality die cast casting can be obtained without changing the die. This is the first object of the present invention.

The above is to reduce the shrinkage cavities by improving the molten metal replenishment property, but it is not sufficiently effective to reduce the cavities of the die casting for filling the molten metal at a high speed. That is, since the injection sleeve in the die casting machine is at a low temperature, when the molten metal from the furnace is poured into this injection sleeve, solidification proceeds immediately from the inner surface of the injection sleeve,
An initial solidified layer of coarse α crystals is formed. When the molten metal in the injection sleeve is pushed by the piston (tip), the initial solidification layer serves as the sliding resistance of the piston, and a predetermined injection pressure is not transmitted to the molten metal. If the pressure propagation of the molten metal is reduced, the suppression of porosity will be insufficient. Of course, preheat the injection sleeve,
Although measures are taken to heat, it is difficult to control the temperature, and if the temperature is set incorrectly, the solidified fragments will enter the gap between the injection sleeve and the piston, increasing the sliding resistance of the piston. Therefore, if a sufficiently high pressure is obtained by taking a metallurgical measure, it is possible to suppress the porosity. This is the second object of the present invention.

[0005]

In order to achieve the first object, the present invention comprises an aluminum alloy for die casting with the following components (1) to (3). 7.5-12 wt% Si 0.4-0.8 wt% Zr 0.4-0.6 wt% Mg or / and 1.5-
4.0 wt% Cu balance Al and unavoidable impurities

In order to achieve the above second object, the present invention provides
The aluminum alloy for die casting is composed of the following components. 7.5-12 wt% Si 0.07-0.16 wt% B 0.4-0.8 wt% Zr or 0.35-0.8
Wt% Ti 0.4-0.6 wt% Mg or / and 1.5-
4.0 wt% Cu balance Al and unavoidable impurities

[0007]

With the addition of Zr, the porosity generated by the solidification of the die surface by the die casting method and the concentration of the porosity at the center of the thickened wall, which is the final solidified portion, is dispersed. By adding Zr, ZrAl _{3 which} is a nucleus of primary crystal aluminum is generated, and solidification uniformly starts from the mold surface to the inside of the wall thickness. Therefore, it is considered that the solidified aluminum crystals were dispersed and the respective aluminum crystal gaps became the final solidified portions and were dispersed as the porosity.

Further, by adding an appropriate amount of B, Ti and Zr, TiAl ₃ , TiB ₂ and ZrAl in the injection sleeve.
₃ · ZrB ₂ is generated to suppress the formation of an initial solidified layer containing coarse α crystals from the inner surface of the injection sleeve. In addition, solid-phase primary crystal aluminum is generated during the process of filling the mold with the molten aluminum from the injection sleeve, so that the solidification shrinkage amount in the mold is reduced, and the decrease of the injection pressure propagation can be suppressed. As a result, a high pressure can be maintained and the cavities can be crushed. Furthermore,
Since the mold can be filled with the molten metal in the fine state of the primary dentrite, the molten metal can contact the mold surface with high density in the fine dentrite state, and can be rapidly cooled to form a sufficiently thick sound layer. .

In the present invention, the preferable composition ratio of each component is as follows. Si: It is an important element that forms a matrix for improving castability and strength, and is set to 7.5 to 12% by weight in consideration of fluidity. When it exceeds 12% by weight, primary crystal Si deteriorates machinability.

Zr: Dentrite nuclei of primary crystal Al are generated. If it exceeds 0.8% by weight, ZrAl ₃ becomes coarse,
If it is less than 0.4% by weight, the effect of addition is not exerted, so
The range is 0.4 to 0.8% by weight. Ti: When it exceeds 0.8% by weight, TiAl ₃ becomes coarse,
If less than 0.35% by weight, the effect of addition is not exhibited,
The range is from 0.35 to 0.8% by weight. Mg: An element that enhances mechanical strength, and is added by 0.4% by weight or more. However, if it exceeds 0.6% by weight, Mg ₂ Si
Is generated and deterioration begins, so the range is 0.4 to 0.6% by weight.

Cu: An element which improves the machinability and strengthens the matrix. In order to exert the effect, 1.5% by weight is necessary, but if it exceeds 4.0% by weight, the corrosion resistance is lowered.
Therefore, the range is from 1.5 to 4.0% by weight. B: Coexists with Ti or Zr to generate nuclei of primary crystal Al. A ratio of Ti or Zr: B = 100: 20 is suitable, and B is 0.07 to 0.16% by weight.

[0012]

EXAMPLES Examples of the present invention will be described below. Die casting conditions common to the examples and comparative examples are as follows. Material Aluminum alloy Casting temperature 680 ° C Casting pressure 130kg / cm ² Gate cross section 1mm × 20mm Injection speed 1.5m / s Mold temperature 150 ° C Product dimensions 17mm diameter × 170mm round bar and 5
2 pieces with 0mm × 180mm × 5mm flat plate Casting weight 450kg

Table 1 shows the dispersibility of the porosity.
TPNo indicates a test piece number.

[0014]

[Table 1]

(Comparative Example) For TP1, 2, 3, and 4, the amount of Zr added was 0.2% by weight, and although not shown in the table, Si = about 1
2% by weight, Mg = about 0.2% by weight and Cu = 2.0% by weight, with the balance being Al as an alloy component.
The voids of 0.5 mm are dispersed about twice as much as the voids of less than 0.15 mm, and the dispersibility of the voids is insufficient.

(Example) For TP11, 12, 13, and 14, the amount of Zr added was 0.4% by weight, and although not shown in the table, S
i = about 12% by weight, Mg = about 0.2% by weight and Cu =
The content is 2.0 wt% and the balance is Al as an alloy component, and most of them have a cavity of less than 0.15 mm, and the dispersibility of the cavity is good.

(Example) For TP21, 22, 23, and 24, the amount of Zr added was 0.6% by weight, and although not shown in the table, S
i = about 12% by weight, Mg = about 0.2% by weight and Cu =
The content is 2.0 wt% and the balance is Al as an alloy component. Similarly, most of them are voids of less than 0.15 mm, and the dispersibility of the voids is good.

(Comparative Example) For TP51, 52, 53, 54, the addition amount of Zr was set to 0% by weight, and although not shown in the table, Si =
About 12% by weight, Mg = about 0.2% by weight and Cu = 2.0
% By weight, with the balance being Al as an alloy component, 0.15
A large number of cavities of -0.5 mm and cavities of more than 0.5 mm were found, and the dispersibility of the cavities was insufficient.

FIG. 1 is a graph showing the relationship between the added amounts of Zr and B and the density of the sound layer, where the horizontal axis is the added amount of Zr and the added amount of B (the added amount of B is 20% of the added amount of Zr), The vertical axis represents the density of the epidermis healthy layer. The test material is Si = 12% by weight, M
g = 0.2% by weight, Cu = 2.0% by weight, Zr = 0 to
0.8% by weight, B = 0 to 0.16% by weight, the balance being Al as an alloy component. According to the figure, 5 mm from the epidermis
It shows that the density up to the thickness increased. The increase in the density of the epidermis having a constant thickness means that the healthy layer is thickened. Therefore, it was confirmed that a good sound layer was obtained when the Zr addition amount was 0.4 to 0.8% by weight.

FIG. 2 is a photomicrograph of the aluminum alloy according to the present invention, which is an 800 times enlarged photo of the Zr addition amount of 0.6% by weight. The needle-shaped body is eutectic Si and the gray ground is the first. Crystalline Al, and the massive crystallized substance in the center of the primary crystal Al is ZrAl ₃ . By adding 0.6% by weight of Zr, ZrAl ₃ is generated, and this ZrAl ₃ serves as a nucleus to solidify Al. It was found that since the nuclei are uniformly distributed from the inner surface of the mold to the center of the wall thickness of the casting, the porosity can be dispersed.

FIG. 3 is a graph showing the relationship between the amounts of addition of Ti and B and the density of the sound layer. The horizontal axis shows the amount of addition of Ti and the amount of B (the amount of B added is equivalent to 20% of the amount of Ti added), The vertical axis represents the density of the epidermis healthy layer. The test material is Si = 12% by weight, M
g = 0.2% by weight, Cu = 2.0% by weight, Ti = 0 to
0.8% by weight, B = 0 to 0.16% by weight, the balance being Al as an alloy component. According to the figure, 5 mm from the epidermis
It shows that the density up to the thickness increased. The increase in the density of the epidermis having a constant thickness means that the healthy layer is thickened. Therefore, the Ti addition amount is 0.35 to 0.8
It was confirmed that a good healthy layer was obtained at a weight percentage.

[0022]

The present invention has the following effects due to the above configuration. Claim 1 defines the composition of the aluminum alloy for die casting as follows: 7.5-12 wt% Si, 0.4-0.8
Since Zr of wt%, Mg of 0.4 to 0.6 wt% or / and Cu of 1.5 to 4.0 wt%, the balance of Al and unavoidable impurities were used, solidification from the die surface by the die casting method. The porosity that begins and concentrates in the thick center that becomes the final solidified portion is dispersed by the addition of Zr. By adding Zr, ZrAl _{3 which} is a nucleus of primary crystal aluminum is generated, and solidification uniformly starts from the mold surface to the inside of the wall thickness.
Therefore, it is considered that the solidified aluminum crystals were dispersed and the respective aluminum crystal gaps became the final solidified portions and were dispersed as the porosity.

According to a second aspect, the composition of the aluminum alloy for die casting is 7.5 to 12% by weight of Si, 0.07 to
0.16 wt% B, 0.4-0.8 wt% Zr or 0.35-0.8 wt% Ti, 0.4-0.6 wt% Mg or / and 1.5- 4.0 wt% Cu,
The balance is Al and unavoidable impurities, and by adding an appropriate amount of B, Ti and Zr, TiAl ₃ , TiB ₂ in the injection sleeve.
And ZrAl ₃ · ZrB ₂ are generated to suppress the formation of an initial solidified layer containing a coarse α crystal from the inner surface of the injection sleeve. In addition, solid-phase primary crystal aluminum is generated during the process of filling the mold with the molten aluminum from the injection sleeve, so that the solidification shrinkage amount in the mold is reduced, and the decrease of the injection pressure propagation can be suppressed. As a result, a high pressure can be maintained and the cavities can be crushed. Furthermore, since the molten metal can be filled into the mold in the fine state of primary dentrite, the molten metal should contact the mold surface with high density in the fine dentrite state and be rapidly cooled to form a sufficiently thick sound layer. You can

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the added amounts of Zr and B and the density of a healthy layer.

FIG. 2 is a micrograph of an aluminum alloy according to the present invention.

FIG. 3 is a graph showing the relationship between the amounts of addition of Ti and B and the density of a healthy layer.

Claims (2)

[Claims] 1. An aluminum alloy for die casting comprising the following components. 7.5-12 wt% Si 0.4-0.8 wt% Zr 0.4-0.6 wt% Mg or / and 1.5-
4.0 wt% Cu balance Al and unavoidable impurities 2. An aluminum alloy for die casting comprising the following components. 7.5-12 wt% Si 0.07-0.16 wt% B 0.4-0.8 wt% Zr or 0.35-0.8
Wt% Ti 0.4-0.6 wt% Mg or / and 1.5-
4.0 wt% Cu balance Al and unavoidable impurities