JPH0819504B2 - Zinc alloy for casting, dimensional change-free, cast parts and heat treatment method for cast parts - Google Patents

Description

Detailed Description of the Invention

[0001]

INDUSTRIAL APPLICABILITY The present invention is suitable for use in the manufacture of zinc alloys for casting, which are free from dimensional change over time, and in particular, precision zinc alloy die-cast parts required in the fields of automobiles, office automation equipment, household appliances and the like. TECHNICAL FIELD The present invention relates to a zinc alloy free of dimensional change over time, a cast part (particularly a die cast part) made of the zinc alloy, and a heat treatment method for the cast part (particularly a die cast part).

[0002]

2. Description of the Related Art Conventionally, cast parts made of zinc alloy, especially die-cast parts, have been widely used as automobile parts such as car body decoration parts, OA equipment parts, parts for home electric appliances and the like. ZDC generally as a zinc alloy for casting for such applications
# 2 (Zn-4% Al-0.04% Mg), ZDC # 1
(Zn-4% Al-1% Cu-0.04% Mg) and the like are used.

[0003]

The parts made of these zinc alloys change their dimensions with age. In order to suppress such dimensional change over time, it is necessary to perform a stabilizing heat treatment, which leads to an increase in cost. However,
The demand for dimensional accuracy in precision zinc alloy die-cast parts is increasing, and the dimensional change over time (in this specification, the dimensional change rate after one year has passed at room temperature) is within ± 0.1%. Is needed.

An object of the present invention is to provide a zinc alloy for casting which does not have the above-mentioned drawbacks, that is, has a dimensional change within a range of ± 0.1%, a cast part made of the alloy, and a heat treatment for the cast part. To provide the law.

[0005]

The inventors of the present invention have conducted various studies in order to solve the above-mentioned problems, and as a result, in the Zn--Al alloy, the magnesium addition amount is set to 0.01% by weight or less, and the copper addition amount is set. It was found that the dimensional change over time can be suppressed within a range of ± 0.1% by making the content of 1% by weight or less, and the present invention has been completed.

That is, the casting zinc alloy of the present invention contains 2 to 10% by weight of aluminum, optionally 1% by weight or less of copper, and further optionally 0.01% by weight of magnesium.
In the following, 1% by weight or less of lithium and 1% by weight or less of beryllium are additionally contained in a total amount of 1% by weight or less, or, if desired, one or more of titanium, cobalt, manganese and lanthanoids are added in a total amount of 0.3. Additional content of less than wt%,
The balance consists of zinc and unavoidable impurities, and is characterized in that the dimensional change over time is within ± 0.1%.

The cast component of the present invention is made of the above zinc alloy for casting.

Further, in the heat treatment method of the present invention, the above cast parts are held in an atmosphere of 70 to 150 ° C. for 1 hour or more,
It is characterized in that a cast part whose dimensional change over time is within ± 0.05 is obtained.

The dimensional change over time of cast parts made of a Zn-Al-Cu-Mg alloy is caused by the Z in the Al phase due to the eutectoid reaction.
It is an aged shrinkage due to the precipitation of n phase, and the amount of shrinkage is Z
It is 0.4 to 0.5% in the case of n-22% Al. Further, the expansion caused by the precipitation of Cu in the Zn phase as the T ′ phase or the ε phase occurs with a time delay. This expansion amount depends on the Cu content, but when the Cu content is 1% by weight or less, such expansion does not occur. Therefore, when the Cu content is 1% by weight or less, only the aged shrinkage due to the above-described eutectoid reaction becomes a problem. This shrinkage reaction will be delayed by the presence of magnesium in the alloy, that is, it will appear as a dimensional change over time during its use as a cast part. Therefore, as a result of performing various tests to obtain the relationship between the shrinkage reaction and the magnesium content,
When the magnesium content is 0.01% by weight or less,
It was found that most of the shrinkage reaction is completed in the cooling process after solidification, and the aging dimensional change can be suppressed within a range of ± 0.1%. In this sense, the technical center of the present invention is to limit the amount of magnesium and the amount of copper.

In the first place, magnesium is generally used in an amount of 0.04 to suppress intergranular corrosion peculiar to Zn-Al alloys.
It is added in an amount of not less than wt%. What is this intergranular corrosion?
This is a phenomenon in which corrosion cracking occurs when impurities such as Pb, Sn, and Cd are mixed in the n-Al alloy.
Therefore, when impurities such as Pb, Sn, and Cd are hardly mixed in the Zn-Al alloy, intergranular corrosion does not occur even if magnesium is not added. Does not occur. When the amount of impurities such as Pb, Sn, and Cd in the Zn-Al alloy is very small (less than usual), addition of 0.01 wt% or less of magnesium can suppress intergranular corrosion. And the magnesium content is 0.0 as described above.
When it is 1% by weight or less, the dimensional change over time is suppressed within a range of ± 0.1%. Therefore, in the alloy of the present invention, magnesium may or may not be added, and when it is added, the addition amount is 0.01% by weight or less.

If desired, one or more of lithium and beryllium may be added to the alloy of the present invention.
Similar to magnesium, these elements are effective in suppressing intergranular corrosion. Since these elements do not suppress aging unlike magnesium, they can be added in a larger amount than magnesium. However, if the added amount exceeds 1% by weight, adverse effects such as embrittlement may occur in terms of strength. Therefore, when the intergranular corrosion inhibiting element is added to the alloy of the present invention, one or more of 0.01 wt% or less of magnesium, 1 wt% or less of lithium and 1 wt% or less of beryllium in total is 1 wt% or less, Preferably 0.1-
0.5% by weight, more preferably 0.01-0.3% by weight
It is desirable to add.

Copper can be added to the alloy of the present invention if desired, and copper is generally effective in improving the strength and hardness of the alloy. Although the properties thereof improve as the copper content increases, as described above, when the copper content exceeds 1% by weight, the alloy tends to expand with time. Therefore, when copper is added to the zinc alloy of the present invention, the amount of copper added is 1% by weight or less.

In the alloy of the present invention, aluminum increases the strength and hardness of the alloy and improves the fluidity of the molten metal. Their properties improve with increasing aluminum content and significant additions of these properties are achieved with additions of 2% by weight or more. Change over time of alloy is ± 0.1
Considering only the fact that it is suppressed within the range of%, it is possible to add a considerably large amount of aluminum, for example, up to 30% by weight, but if the aluminum content is too high, the melting point of the alloy becomes high and the die casting The possible temperature will be higher. Therefore, in the zinc alloy of the present invention, the amount of aluminum added is 2% by weight or more and 10% by weight or less, which allows hot chamber die casting, and preferably 3.5 to 8% by weight.

In the alloy of the present invention, if desired, one or more elements selected from the group consisting of titanium, cobalt, manganese and lanthanoids can be added in an amount of 0.3% by weight or less. Are all commonly used elements that have the effect of improving mechanical strength. However, if the addition amount thereof exceeds 0.3% by weight, adverse effects such as embrittlement may occur in terms of strength. Therefore, when those elements are added to the alloy of the present invention, one or more kinds of titanium, cobalt, manganese and lanthanoid are added in a total amount of 0.3% by weight or less.

In the alloy of the present invention, the dimensional change over time can be further reduced by a simple heat treatment. That is, a cast part made of the alloy of the present invention is placed in an atmosphere of 70 to 150 ° C., for example, in water of 70 to 100 ° C. or 70 to 150 ° C.
By holding in air at 150 ° C., preferably in water at 70 to 100 ° C. for 1 hour or more, it is possible to obtain a cast component having a dimensional change within a range of ± 0.05. By this heat treatment, the shrinkage reaction that has not been completed in the cooling process after solidification can be completely completed. This heat treatment is only to immerse the cast parts in hot water during the process, and does not lead to a cost increase.

Examples 1 to 7 and Comparative Examples 1 to 3 In a graphite crucible, electrolytic zinc as a base and a required amount of A were used.
l, Cu, Mg and other additive components were charged and melted to prepare an alloy having the alloy components and the composition (% by weight) shown in Table 1 (including inevitable impurities). 100m length from the molten alloy under the following die casting conditions
m, 10 mm square, and the end surface were machined to make a test piece: Toshiba 135ton cold chamber die casting pressure 95 kgf / cm ² mold temperature 180-190 ° C The die casting temperature is the lowest temperature at which a sound casting can be obtained for each alloy. Settings These die-cast test pieces (Examples 1 to 6 and Comparative Examples 1 to 3) and test pieces immersed in 100 ° C. hot water for 1 hour (Example 7) were held in air at 60 ° C. for 1 year. During this period, appropriate dimension measurement was performed to obtain the maximum dimension change. The results were as shown in Table 1.

[0017]

[Table 1] Example No. Composition Composition change over time Comparative example 1 Zn-4Al- 0.04 Mg (ZDC 2) -0.23 Example 1 Zn-4Al- 0.01 Mg -0.08 Example 2 Zn-4Al-0. 05 Comparative Example 2 Zn-4Al-1Cu- 0.04 Mg (ZDC 1) -0.28 Comparative Example 3 Zn-4Al-2Cu- 0.04 Mg +0.42 Example 3 Zn-4Al-1Cu- 0.01 Mg -0.09 Implementation Example 4 Zn-5Al-1Cu-0.01 Mg -0.09 Example 5 Zn-8Al-1Cu- 0.02 Li -0.06 Example 6 Zn-8Al-1Cu- 0.02 Be -0.06 Example 7 Zn-5Al -1Cu-0.01 Mg-0.0025

Within the range of the above embodiment, the copper content is 0.
-1% by weight and a magnesium content of 0-0.01% by weight of a die-cast test piece made of a Zn-Al alloy is within ± 0.09%, and a heat-treated die-cast test is performed. Change over time of one piece is ± 0.003
%, The aging dimensional change of the die casting test piece made of the Zn-Al alloy of the present invention is within ± 0.1% even if the composition change of the alloy is taken into consideration. It is clear that the secular dimensional change of the pieces is within ± 0.05%.

[0019]

The aging dimensional change of the zinc alloy for casting of the present invention is within the range of ± 0.1%, which is a zinc alloy free from aging dimensional change suitable for use in the production of precision zinc alloy die casting parts. Therefore, it can be used for a wide range of purposes.

Front page continuation (72) Inventor Koji Hoshitani 2 1333, Ojiwara, Ageo City, Saitama Prefecture Mitsui Mining & Smelting Co., Ltd. (72) Inventor Kiyotaka Yanagi 2 1333, Ojihara, Ageo City, Saitama Mitsui Mining Co., Ltd. Company Research Institute (56) References Japanese Patent Publication Sho 34-2256 (JP, B1)

Claims (8)

[Claims] 1. A content of aluminum is 2 to 10% by weight, copper and magnesium are not contained, and the balance is zinc and unavoidable impurities, and the dimensional change over time is within ± 0.1%. Zinc alloy for casting. 2. Aluminium 2 to 10% by weight and copper 1% by weight or less, magnesium is not included, the balance is zinc and inevitable impurities, and the dimensional change over time is within ± 0.1%. Zinc alloy for casting characterized by. 3. Magnesium 0.01% by weight, characterized by containing additional Li Chi <br/> um 1 wt% or less, and beryllium 1 wt% or less than 1% by weight of one or more of the total billing The zinc alloy for casting according to Item 1 or 2. 4. The zinc alloy for casting according to claim 1, further comprising 0.3% by weight or less in total of one or more of titanium, cobalt, manganese and lanthanoid. 5. A cast part made of the alloy according to claim 1. 6. A component according to claim 5, wherein the cast component is a die cast component. 7. The cast component according to claim 5 or 70
A heat treatment method for cast parts, which is characterized by holding in an atmosphere of 150 ° C. for 1 hour or more to obtain cast parts having a dimensional change within a range of ± 0.05%. 8. An atmosphere of 70 to 150 ° C. is 70 to 10
The heat treatment method according to claim 7, which is in water at 0 ° C.