JPH01147035A - Alloy having low aging characteristics - Google Patents

Abstract

PURPOSE:To manufacture the title alloy useful as the material of a mold for molding of plastics by adding a specific amount of Sr to a zinc-based alloy contg. specific ratios of Al, Cu and Mg. CONSTITUTION:50-200ppm Sr, by weight, is added to the zinc-based alloy consisting of 9-15% Al, 7-12% Cu, 0.01-0.1% Mg and the balance Zn consisting substantially of Zn with inevitable impurities. By this method, the alloy for a mold having excellent mechanical strength, having small dimensional and physical change by aging and easily executable of casting and working is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a low aging alloy that can be used as a mold mainly used for molding plastics.

(Prior Art) In recent years, the housings, parts, etc. of various devices such as OAi devices have been made of plastic, and model changes have been frequently made to improve the performance of the devices.

Along with this trend, molding cycles for plastic products are being shortened and high-mix low-volume production is being implemented.

For this reason, new materials that are easy to cast and process are required for plastic molds in place of conventional materials.

Traditionally, metals such as cast iron and cast steel have been used for plastic molds, especially injection molds, but although these metals have excellent mechanical strength, they are difficult to cast and process. , Due to the high casting temperature, large-scale equipment is required for casting.

Further, since casting is performed in a sand mold, the surface of the cast product becomes rough, and therefore a large number of man-hours are required for surface polishing.

Moreover, in order to manufacture a precise mold, a large amount of time is required for machining such as cutting and electrical discharge machining.

Therefore, copper alloys are used instead of cast iron and cast steel, but copper alloys have high casting temperatures, so casting requires equipment and treatments such as oxidation prevention, and the casting temperature is 1ooo''.
Since the temperature exceeds C, plaster cannot be used for the mold, and a ceramic mold is used.

Ceramic molds are expensive and difficult to manufacture.

Moreover, copper alloys require long electrical discharge machining, just like cast iron and cast steel.

In order to solve these drawbacks, we developed a mold material for plastic molding that has a low casting temperature and is easy to cast and process.
Zinc alloys have been proposed.

This zinc alloy is a zinc alloy for die casting (ZDC-1
), and contains aluminum, copper, magnesium, etc. in addition to zinc.

For example, Japanese Patent Publication No. 51-5342 G discloses a wear-resistant zinc-based alloy consisting of aluminum, copper, magnesium, beryllium, titanium, silver, and the balance zinc.

(Problems to be Solved by the Invention) However, these zinc-based alloys have insufficient mechanical strength, and the magnesium added for the purpose of preventing intergranular corrosion causes dimensional deformation due to aging, causing plastics to deteriorate. When used as a mold, there is a risk of cracks occurring on the surface of the mold.

Further, as molding operations are repeated using this mold, the accuracy of the mold decreases, and there is a risk that so-called burrs may occur in the molded product, so that it can only be used as a prototype mold.

Therefore, in order to further increase the strength of the alloy, it is conceivable to increase the content of aluminum or copper.

In particular, the addition of aluminum and copper has a remarkable effect on increasing strength.

However, as the amount of these elements added increases, dimensional changes and strength decreases due to aging increase.

In particular, the dimensional change caused by copper can sometimes reach 1%, and the actual situation is that it is not suitable not only for precision molds but also for molds with complex shapes.

Further, in this case, copper has an effect on mechanical strength, but because of its high phase transformation temperature, it has drawbacks such as difficulty in applying methods such as solution treatment.

The present invention solves the above-mentioned conventional problems, and its purpose is to provide a material with excellent mechanical strength, small changes in dimensions and physical properties due to aging, easy casting and processing, and rapid processing. The purpose of the present invention is to provide an alloy for molds that can be manufactured.

(Means for Solving the Problems) The present invention improves mechanical strength by adding a small amount of strontium to a conventional zinc-based alloy containing aluminum, copper, and a small amount of magnesium. The main purpose is to suppress volumetric swelling due to precipitation and minimize the effects of aging (dimensional changes, strength reduction).

The zinc-based alloy of the present invention contains 9 to 15% by weight of aluminum,
The above purpose can be achieved by adding 50 to 200 ppm of strontium by weight to a zinc-based alloy consisting of f17 to 12% by weight, magnesium 0.01 to 0.1% by weight, and the remainder mainly consisting of zinc and unavoidable impurities. is achieved.

As in the present invention, zinc is the main component, and zinc forms alloy crystals with each contained element and precipitates as minute crystals, but in the case of alloys containing considerable amounts of aluminum and copper,
Due to changes over time or the influence of heat, crystal changes occur slowly, resulting in a phenomenon called aging (dimensional change, decrease in physical properties).

The small amount of strontium added in the present invention generally tends to concentrate in metals, especially in alloys containing a large amount of aluminum as in the present invention, at the crystal grain boundaries (crystal interfaces) of the metal, and as a result, the zinc alloy It has the effect of suppressing crystal growth and enlargement.

Therefore, the above strontium is the Zn-Al-
It suppresses crystal growth of the Cu-Mg zinc-based alloy, keeps the zinc-based alloy in a microcrystalline state, improves mechanical strength, and suppresses deterioration of physical properties and dimensional changes due to aging.

In addition, the amount of strontium added is set at 50 to 200 ppm by weight relative to the above zinc-based alloy; if it is too little, it will not be effective, and if it is too much, hardness will increase but brittleness will develop. , mechanical strength decreases.

In order to fully exhibit the effect of adding strontium, it is preferable to add strontium after degassing the molten alloy.

It is known that magnesium also precipitates at grain boundaries and is particularly effective in preventing intergranular corrosion, but especially when a small amount of magnesium coexists as in the present invention, the grain boundaries are fixed and the alloy It is thought to have a strong effect of inhibiting crystal growth.

This effect occurs when the amount of added magnesium is small; when a large amount is added, it interferes with grain boundary precipitation of added strontium, so care must be taken in the amount of magnesium and strontium added.

Therefore, the amount of magnesium added is 0.01 to 0.1% by weight.

The amounts of aluminum and copper to be added should be 9 to 15% by weight and 7 to 1% by weight, respectively, in order to fully exhibit their addition effects.
The amount is 2% by weight, and if it is too little, the mechanical strength and hardness will be insufficient, and if it is too much, the hardness will increase but brittleness will develop.

Incidentally, unavoidable impurities here refer to unavoidable impurities, even if the purest zinc ingot, which is normally used as a zinc alloy for Gui casting, is used as a raw material.
In addition, it refers to all elements that are unavoidably mixed in during the refining process and all elements that may be mixed in from the outside during the casting process, etc. Specifically, as specified in JIs-H5301 type, weight percentage and PbO,007 or less, F e 0
．． 10 or less, Cd 2 O, OO5 or less, Sn 0.005 or less, and up to a total of 0.05% of all metals and metalloid elements not listed in the claims.

(Example) Examples of the present invention will be described below.

Examples 1 to 6, Comparative Examples 1 to 6゜ Predetermined amounts of zinc, aluminum, copper, and magnesium were sufficiently dissolved to form an alloy with a uniform composition, and a degassing agent containing chlorine and hexachloroethane was added. After removing the dissolved gas in the molten metal, the oxides and slag separated from the molten metal were removed.

Next, a predetermined amount of aluminum-strontium alloy was added to the above alloy and uniformly melted to produce an alloy having the composition shown in Table 1.

From this alloy, Jl5-H5301 tensile test piece (1) shown in reference figure A and hardness test piece (1) shown in reference figure B were prepared.
2) was created.

The tensile strength (kg/ml1') of this test piece (1) immediately after casting (within 30 hours after casting) is in accordance with JIS-Z224.
Measured according to 1.

In addition, the purinnel hardness (HB) of the test piece (2) was determined according to JIS-
The length was measured according to Z2243.

The above test pieces (1) and (2) were heat treated at 200''C for 24 hours to complete aging, and then tensile strength, hardness, and length were measured in the same manner.

The above measurement results are shown in Table 2.

(The following is a margin) Table 1 (The units of AI, Cu, and Mg are weight %, and including Zn, it becomes 100 weight %.

Sr is l) relative to the total amount of AI, Cu, Mg and Zn.
pm) Table 2 (blank below) From the above results, Zn-Al-
It is clear that changes in properties and dimensions due to aging are suppressed by adding strontium to Cu-Mg zinc-based alloys.

(Effects of the Invention) Since the low aging alloy of the present invention has the above-mentioned structure, it has improved mechanical strength, and does not reduce mechanical strength due to aging without impairing castability or workability. Decrease in hardness and dimensional change can be suppressed.

Therefore, when this alloy is used as a plastic mold, there is no risk of cracks occurring on the surface, and the precision of the mold will not deteriorate even after repeated molding operations.
Very useful as a material for plastic molds.

Claims (1)

[Claims] 1. By weight percentage, aluminum 9-15%, copper 7-1
2%, magnesium 0.01-0.1%, the balance mainly consisting of zinc and unavoidable impurities,
A low aging alloy characterized in that strontium is added in a weight ratio of 50 to 200 ppm.