JPH0254408B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Field of Application) The present invention relates to the production of a molded body of Al-Si alloy powder, and more particularly to a method for producing a powder compact having excellent toughness such as notch strength. (Conventional technology and problems to be solved) Al-Si alloy powder takes advantage of the lightness of aluminum alloy and has excellent performance such as high strength, high rigidity, and wear resistance. It is used in a wide range of applications such as automobiles, aircraft, robots, etc., which require lightweight members with excellent mechanical properties, and is usually manufactured in the form of billet extrusion molded products. This Al-Si alloy powder is mainly a hypoeutectic Al-Si alloy containing about 10% Si or a hypereutectic Al-Si alloy containing about 12% Si, especially hypereutectic Al-Si alloy powder. Si-based alloys have excellent heat resistance and wear resistance. However, on the other hand, powder compacts of hypereutectic Al-Si alloys have poor elongation near room temperature and low ductility, so they are used in parts, especially those with complex shapes or under severe stress conditions. In the case of such members, there was a problem in that they were prone to breakage at stress concentration areas and lacked safety and reliability. The present invention eliminates the drawbacks of the above-mentioned prior art, and provides excellent performance such as strength and wear resistance.
The object of the present invention is to provide a method for producing an Al-Si alloy powder compact having excellent notch strength and ductility. (Means for solving the problem) In order to achieve the above object, the present inventor has developed a conventional
When we investigated the properties of Al-Si alloy powder compacts, we found that, especially in the case of hypereutectic Al-Si alloy powder,
The alloy structure of the powder revealed that eutectic Si was precipitated in the form of needles or plates. Therefore, as a result of various research into ways to improve ductility by changing the alloy structure of such powder, we found that the eutectic Si having an acicular or plate-like structure as described above can be made into a moderately spherical shape by heat treatment. We have found that it is effective to That is, in the method for producing an Al-Si alloy powder compact according to the present invention, for Al-Si alloy powder,
The preform is heat-treated at 470 to 500°C for 0.5 hours or more and then hot-formed.
It is characterized by heat treatment at 470 to 500°C for 0.5 hours or more. The present invention will be explained in detail below based on examples. As mentioned above, in the case of billet extrusion, Al--Si alloy powder compacts have conventionally been produced by heating and extruding a billet at a temperature of about 400°C. In contrast, in the method of the present invention, heat treatment is performed under predetermined heating conditions immediately before hot forming (preformed body) or after hot forming of the preformed body. The preforming may be hot preforming (eg, 250° C.) as shown in FIG. 1, or cold preforming. As for hot forming, in addition to extrusion forming (for example, at 400° C.) as shown in Examples below, forging is also possible. As for the heating conditions, it is necessary to heat at a temperature of 470° C. or higher, preferably 480 to 500° C., in order to spheroidize the eutectic Si having an acicular or plate-like structure in the material. The heating time is preferably 0.5 hours or more at 470° C. or higher, and suitably about 0.5 to 2.0 hours. It may be heated for a longer time (e.g. 5 to 6 hours or more), but
No further effect can be obtained, and heating for too long is undesirable because the structure becomes coarser and the ductility deteriorates. The temperature and holding time at 470° C. or higher may be selected in consideration of the timing of heat treatment (immediately before extrusion processing or after processing), material composition, etc. Note that there is no particular difference in the effect depending on the timing of heat treatment. The composition of the Al-Si alloy powder to be subjected to the above heat treatment is not particularly limited, but the strength,
Hypoeutectic in terms of performance such as wear resistance and heat resistance
Al-Si alloys and hypereutectic Al-Si alloys are preferable.
In addition, the effects of the present invention are further exhibited. For example, the Si content is preferably 10.0 to 30.0%,
14.0 to 25.0% is more preferable, and one or more of Fe, Mn and Ni may be added in an amount of 1.0 to 15.0%, preferably 5.0 to 10.0%, in order to increase the high temperature strength. Ti, Zr, Mo, V, Cr, Zn,
Addition of a small amount of Li or the like also has the effect of improving high temperature strength. Furthermore, Mg and Cu may be added as components to strengthen the material. The Al--Si alloy powder may be produced by a commonly used method, such as an atomization method and a pulverization method using centrifugal force. Moreover, billet extrusion may be performed under normal conditions. Of course, when heat treatment according to the present invention is performed immediately before processing (pre-treatment), an appropriate temperature for processing must be ensured following the heating cycle, and when heat treatment is performed after processing (post-treatment). Needless to say, the powder compact must be subjected to a heating cycle after processing. (Example) Molten hypereutectic Al--Si alloy powders having the compositions shown in Table 1 were air atomized to obtain powders of -48 mesh. Next, these alloy powders are heated to 250℃
and fill it into a mold preheated to the same temperature.
Compression molding was performed at a pressure of 1.5 ton/cm ² to form a billet with a diameter of 100 mm and a length of 200 mm. Next, extrusion molding and heat treatment were performed under the conditions shown in Table 2 and FIG. 1 to produce an extruded material (round bar). For extrusion, the billet temperature was set at 400°C, inserted into a container preheated to the same temperature, and formed into a round bar at an extrusion ratio of 17. The extruded material produced under these conditions was subjected to a tensile test and a notched tensile test at room temperature to evaluate its properties. The tensile test piece has a diameter of 3 mm and a parallel part.
The size of the notched tensile test piece shall be 16 mm.
A 60° notch with a diameter of φ and a depth of 1 mm was made, the radius of curvature at the tip was 0.45, and the notch strength was measured in a stress state with a stress concentration factor of 2. Those results in the third
Shown in the table. As is clear from Table 3, when using the conventional method (processing conditions A), high tensile strength is obtained but the notch strength is inferior, whereas when using the present invention method (processing conditions B and C), the notch strength is poor. The strength is markedly improved, and the tensile strength is also maintained at approximately the same level, with no loss of tensile properties.

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[Table] (Effects of the invention) As detailed above, according to the present invention, Al-
A simple method of heat-treating a Si-based alloy powder compact at a specific temperature allows us to improve ductility such as notch strength without sacrificing its excellent performance such as lightweight, high strength, high rigidity, wear resistance, and heat resistance. Since it can significantly improve safety and reliability, it is particularly suitable for manufacturing parts with complex shapes or parts used under severe stress conditions, and we aim to further expand its use in various fields. becomes possible.

[Brief explanation of drawings]

FIG. 1 is a diagram showing extrusion and heat treatment conditions for an Al--Si alloy powder compact, where a shows the case of the conventional method, and b and c each show the case of the method of the present invention.

Claims (1)

[Claims] 1. A preformed body of Al-Si alloy powder
A method for producing an Al-Si alloy powder compact having excellent notch strength, the method comprising heating at 500°C for 0.5 hours or more and then hot forming. 2. A method for producing an Al-Si alloy powder compact with excellent notch strength, which comprises heating a preform of Al-Si alloy powder at 470 to 500°C for 0.5 hours or more after hot forming. .