JPH0959738A - Aluminum alloy casting for sliding member excellent in strength and wear resistance and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To micronize primary-crystal Si, to improve strength, and to provide excellent wear resistance by specifying the composition of a hyper-eutectic Si-aluminum alloy of JIS-AC9A or -AC9B type and performing pressure casting and then aging treatment. SOLUTION: An alloy, having a composition consisting of, by weight ratio, 16.5-25% Si, 2.0-6.0% Cu, 0.5-1.0% Mg, 0.4-1.0% Mn, 0.5-1.2% Zn, <=200ppm Ca, and the balance Al with inevitable impurities, is used. A molten alloy of this composition is poured into a metal mold, solidified under a pressure as high as >=500kgf/cm<2> , and then subjected to solution heat treatment, hardening, and aging treatment, by which a casting of >=Hv180 hardness is formed. By the above treatment, hard and fine primary-crystal Si is uniformly dispersed and wear resistance and thermal expansion resistance can be improved. Further, the occurrence of casting defects, such as porosity and crack, can be prevented and also stable mechanical properties can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to compressor parts or engine parts used for car coolers,
The present invention relates to a suitable aluminum alloy casting for a sliding member such as a shift fork, and more specifically, an aluminum alloy casting for a sliding member having improved strength and wear resistance as compared with a conventional aluminum alloy casting for the same purpose and a method for producing the same. Regarding

[0002]

2. Description of the Related Art Sliding members are required to have a high wear resistance on their sliding surfaces. Therefore, cast iron, hardened steel, aluminum bronze, etc. are conventionally used, and the sliding surface is plated or anodized. Some were processed. However, in recent years, it has been required to reduce the weight and size of all parts, and a lightweight aluminum alloy is often used also for the sliding member. Aluminum alloys used as these sliding members are JIS AC9A, AC9
B or a hypereutectic Si alloy containing about 15 to 20% by weight of Si (such as A390 of AA (American Aluminum Association) standard) (hereinafter, weight% is simply abbreviated as "%"), which is mainly used for die casting or die casting. Manufactured by law. Also, it is produced as a casting rod by the continuous casting method,
In some cases, the product shape is forged as it is or after extrusion. However, since the product obtained by the die casting has a slow solidification rate, primary crystal silicon is coarsened, and there is a problem that strength, particularly toughness deteriorates and machinability deteriorates.
In addition, the die casting method, which has a proven track record in some shift forks and engine blocks, allows the molten metal to be rapidly cooled, so the primary crystal silicon becomes fine, but many gas casting defects peculiar to die casting, solidification chill layers, and other casting defects, Stable and sufficient toughness and toughness cannot be obtained.

Further, the casting rod produced by the continuous casting method has few internal defects and is a good material, but if the Si content exceeds 18%, the continuous casting itself becomes substantially difficult. Moreover, in order to obtain a final product using this material, it is usually a continuous casting rod (in some cases, further extruded rod).
Often used after cutting the material into an appropriate length by forging, many processes such as preforming, roughing and finishing are performed, resulting in poor yield and tool wear during cutting. However, there is a drawback that the manufacturing cost at the time of cutting becomes high.

Since weight reduction efficiency and cost reduction are indispensable for the recent aluminumization, it is strongly desired to develop a casting material having the same performance as a forged material and capable of reducing the cost. Recently, attempts have been made to overcome casting problems by the high pressure casting method so as to satisfy this demand. The high-pressure casting method is a method in which the molten metal is filled into the mold at a low speed and pressure is applied continuously until the solidification is completed. The advantage is that stable mechanical performance can be obtained. Further, since the cooling rate is high as in the die casting method, there is an advantage that the primary crystal Si grain size becomes fine. However, in the case of thick-walled parts, a region with little or no primary crystal Si (hereinafter referred to as a surface chill layer) is generated in the surface layer, while primary crystal Si is coarsened in the final solidified portion such as the sprue or the center part of the wall thickness. May give rise to areas.

In many cases, a casting material is machined on its sliding surface or mechanical joining surface depending on the shape of the product. At that time,
Coarse Si particles promote tool wear during machining and also deteriorate the finished state of the machined surface. Further, if a surface chill layer containing almost no primary crystal Si is locally present on the surface of the product, the abrasion resistance when used as a sliding member may be significantly deteriorated. Therefore, in the casting material,
It is required that primary crystal Si of a certain size that does not impair machinability be dispersed uniformly regardless of location while ensuring wear resistance. Therefore, CuP or phosphorus-based flux is usually added to the molten metal as an improvement treatment material for refining the primary crystal Si, but it is necessary to keep it at a high temperature of 800 ° C. or higher in order to obtain a sufficient improvement treatment effect. Therefore, due to the increase in the amount of hydrogen gas in the molten metal, gas defects are more likely to occur, the furnace material is easily worn, the production efficiency is reduced, or it is necessary to add an expensive improved treatment material. ,
There are problems such as an increase in manufacturing cost.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above problems and provide an aluminum alloy casting for sliding members which is excellent in strength and wear resistance and can be manufactured at low cost, and a manufacturing method thereof. To do. Specifically, without using the above-described improved treatment material for refining the primary crystal Si, the primary crystal Si is refined over the entire casting, that is, in the vicinity of the sprue, the central portion of the wall thickness and other parts, and its distribution is appropriate. And to further improve the strength of the matrix itself, to obtain an aluminum alloy casting for sliding members having excellent strength and wear resistance, and a method for producing the same.

[0007]

According to the invention of claim 1 for solving the above-mentioned problems, Si16.5 to 25%, Cu2.
0-6.0%, Mg 0.5-1.0%, Mn 0.4-
An aluminum alloy containing 1.0% and 0.5 to 1.2% Zn, further controlling Ca to 200 pmm or less, and the balance being aluminum and unavoidable impurities, and having a hardness Hv of 180 or more. It is an aluminum alloy casting for sliding members which is characterized by having excellent strength and wear resistance, and the invention of claim 2 is Si 16.5 to 25%, C
u2.0-6.0%, Mg0.5-1.0%, Mn0.
4 to 1.0%, Zn 0.5 to 1.2%, and further C
a is regulated to 200 ppm or less, the balance is filled with an aluminum alloy molten metal composed of aluminum and unavoidable impurities, and solidified under a high pressure of 500 kgf / cm ² or more, then solution heat treatment, quenching, A method for producing an aluminum alloy casting for sliding member, which is excellent in strength and abrasion resistance, characterized in that a material hardness Hv is 180 or more by performing an aging treatment.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail. In the invention of claim 1, the composition of the alloy is as described above for the following reason. Si
Is an element effective for improving the abrasion resistance and the thermal expansion resistance as crystallized as hard primary crystal Si, but if the addition amount is less than 16.5%, there is no effect, and if it exceeds 25%. When the casting temperature is 750 ° C. or higher, the amount of dissolved gas in the molten metal increases, gas defects are likely to occur, and damage to the furnace material is likely to occur, which is a practical problem. Therefore, Si is set to 16.5 to 25%.

Cu and Mg are both effective elements for improving the strength, but their added amounts are 2.0% and 0.5, respectively.
If it is less than%, sufficient strength cannot be obtained, and conversely 6.0
% And 1.0%, eutectic melting tends to occur easily during solution heat treatment for strength imparting.
Corrosion resistance deteriorates. Therefore, Cu is 2.0 to 6.0%, M
g is 0.5 to 1.0%. Mn combines with a needle-shaped aluminium-iron-based compound that crystallizes as an unavoidable impurity in aluminum to form a lump-shaped aluminium-iron-manganese-based compound, and as a result, acts to improve the toughness of the material. If the added amount is less than 0.4%, the above effect does not occur and 1.0%
If it exceeds the range, a coarse compound is produced and the toughness deteriorates. Therefore, Mn is 0.4 to 1.0%.

Zn forms a solid solution in the matrix and improves the strength and hardness after heat treatment, and is effective in improving wear resistance. If the added amount is less than 0.5%, the above effect does not occur,
If it exceeds 1.2%, solidification cracking tends to occur and the corrosion resistance deteriorates. Therefore, Zn is 0.5 to 1.2%. Further, since Ca contained as an impurity is likely to generate feather-like coarse primary crystal Si grains and significantly impairs machinability, the amount of Ca needs to be regulated to 200 ppm or less. Fe, which is contained as another impurity, is not preferable because it crystallizes as an acicular intermetallic compound, but since its effect is mitigated by the simultaneous addition of Mn, mixing up to 1.0% is not a problem. In the invention of claim 1, in addition to the above requirements, the hardness of the material is set to 180 or more in Hv, but such hardness of the material remarkably improves wear resistance. This is because.

Next, in the invention of the manufacturing method according to claim 2, when the molten aluminum alloy having the above composition is filled in a mold and solidified, solidification under a high pressure of 500 kgf / cm ² or more is a porosity. This is to reduce the internal defects of the casting such as shrinkage cavities and casting cracks and to obtain sound internal quality. If the casting pressure is less than 500 kgf / cm ² , these internal defects occur and the mechanical performance deteriorates. Therefore, it is necessary to solidify at the above-mentioned pressure. In addition, in the production method of the present invention, after solidification under the above-mentioned high pressure, heat treatment is performed to improve mechanical properties. That is, solution heat treatment, quenching, and aging treatment are performed. This heat treatment condition is not particularly limited, and the hardness of the material is set to 180 or more in Hv by carrying out under normal treatment conditions. The hardness of the material is set in this way in order to impart abrasion resistance for the sliding member as described above.

[0012]

The present invention will be described below in detail with reference to examples. First, the casting apparatus shown in FIG. 1 was used for casting. This casting apparatus has a cavity portion (product portion) 2 formed in a mold 1.
It comprises a molten metal supply path 3, an injection sleeve 4 into which a fixed amount of molten metal is poured, and a plunger tip 5 which moves inside the injection sleeve to fill and pressurize the molten metal in the cavity portion.
Here, a water cooling pipe 6 is passed through the mold 1 at regular intervals along the cavity so that the amount of water cooling can be changed depending on the location. Here, the aluminum alloys having the compositions shown in Table 1 were melted by a normal method, degassed by Ar gas bubbling for about 20 minutes at a melt temperature of 750 ° C.
Pressure casting is performed under the casting conditions shown in, and the wall thickness is 20 mm and width is 1.
A flat plate test piece having a length of 00 mm and a length of 200 mm was prepared. The mold temperature during casting was controlled by changing the amount of water in the water-cooled pipe at each site while casting.

[0013]

[Table 1]

[0014]

[Table 2]

The cross sections of these aluminum alloy castings were polished, and internal defects such as shrinkage cavities and casting cracks were observed with a stereoscopic microscope. Further, after subjecting the test piece to solution heat treatment at 490 ° C. for 4 hours, water cooling, aging treatment at 180 ° C. for 8 hours, hardness Hv (Vickers hardness) of the cross section of the casting
Was measured. Further, a tensile test piece and a Charpy test piece were sampled, and a Charpy impact value which was an index value of tensile strength, elongation value and toughness was measured. Similarly, a test piece was cut out and a specific wear amount, which is an index value of wear resistance, was measured using an Ogoshi-type wear tester. Table 2 shows the results.

As is clear from Table 2, no internal defects were observed in the test pieces obtained by casting the alloy having the composition according to the present invention under the predetermined casting conditions, and A390 which has been conventionally used for sliding members is used. It is clear that both strength and toughness are superior to alloy castings. Further, the alloy casting according to the present invention has a hardness Hv of 180 or more, which is higher than that of conventional alloy castings.
It can be seen that the specific wear amount is small and the wear resistance is also excellent. On the other hand, when the alloy composition deviates from the scope of the claims of the present application, sufficient strength and toughness cannot be obtained, and wear resistance is poor. Further, even when the alloy composition is within the scope of the claims of the present application, if the casting pressure is low, internal defects such as shrinkage cavities and casting cracks frequently occur in the product, and stable mechanical performance cannot be obtained.

[0017]

As described above, according to the present invention, compared with the conventional aluminum alloy castings, the cost is low and the wear resistance is excellent.
In addition, since it is possible to obtain a sound casting with no internal defects remaining, it can be used for sliding members such as compressor parts and engine parts, and it is possible to reduce the manufacturing cost with the same performance as forging material. It is effective.

[Brief description of drawings]

FIG. 1 is a pressure casting apparatus according to an embodiment of the present invention,
It is a schematic sectional drawing of the principal part for the description.

[Explanation of symbols] 1 Mold 2 Cavity part (product part) 3 Molten metal supply path 4 Plunger sleeve 5 Plunger tip 6 Water cooling pipe 7 Gas vent

Claims (2)

[Claims] 1. Si 16.5 to 25 wt% (hereinafter wt% is simply abbreviated as%), Cu 2.0 to 6.0%, Mg 0.
5 to 1.0%, Mn 0.4 to 1.0%, Zn 0.5 to
An aluminum alloy containing 1.2%, further limiting Ca to 200 ppm or less, the balance being aluminum and unavoidable impurities, and having a material hardness Hv of 180 or more. Aluminum alloy castings for sliding parts with excellent wear resistance 2. Si 16.5 to 25%, Cu 2.0 to 6.
0%, Mg 0.5 to 1.0%, Mn 0.4 to 1.0%,
Zn 0.5-1.2% is included, and Ca is further added at 200 pp.
It is regulated to m or less, and the mold is filled with a molten aluminum alloy whose balance is aluminum and unavoidable impurities.
Excellent in strength and abrasion resistance, characterized by setting the hardness Hv of the material to 180 or more by solidifying it under a high pressure of 500 kgf / cm ² or more and then subjecting it to solution heat treatment, quenching, and aging treatment. Manufacturing method of aluminum alloy casting for sliding member