Metal matrix composite casting and manufacturing method thereof

Details Metal matrix composite casting and manufacturing method thereof Metal matrix composite casting and manufacturing method thereof

1998-05-27

2001-06-12

Jones, Deborah (Department: 1775)

Stock material or miscellaneous articles

All metal or with adjacent metals

Laterally noncoextensive components

C428S596000, C428S600000, C428S653000, C428S469000, C361S704000, C361S719000, C257S707000, C257S717000, C257S720000

Reexamination Certificate

active

06245442

ABSTRACT:

CROSS REFERENCE TO RELATED APPLICATION
This application is based upon and claims the benefit of priority from Japanese patent applications No. H. 9-155823 filed on May 28, 1997, No. H.9-288938 filed on Oct. 21, 1997, No. H.10-64613 filed on Feb. 26, 1998, and No. H.10-72690 filed on Mar. 20, 1998, the contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a metal matrix composite casting in which particles, fibers, short fibers, whiskers or the like of, for example, ceramic are dispersed and a manufacturing method thereof.
2. Related Art
Metal matrix composites are materials formed by dispersing a property-improving materials such as particles and fibers in a metal serving as a host material. As one example of the metal matrix composites, there is an aluminum matrix composite in which ceramic particles are dispersed in aluminum. In a manufacturing process of the aluminum matrix composite, a preform of the ceramic particles is disposed in a casting metal mold and is incorporated within aluminum by die-casting.
The aluminum matrix composite is used, for example, as a part functioning as a heat-sink for a semiconductor power module. For a metal matrix composite functioning as a heat-sink, an aluminum-silicon carbide (Al-SiC) composite is generally used. Because of the necessity of mounting an IC substrate on the heat-sink, the heat-sink must be subject to a secondary process such as a surface finishing process and a hole forming process. However, since the Al-SiC composite is very hard, it is difficult to carry out the secondary process with respect to the Al-SiC composite, and therefore, the cost thereof becomes high.
In view of the problem discribed above, a method in which the surface of the Al-SiC composite is processed by utilizing an Al layer formed in the surface thereof at the time of manufacturing the Al-SiC composite has been proposed. U.S. Pat. No. 5,234,045, U.S. Pat. No. 5,570,502, U.S. Pat. No. 5,616,421)
In this method, however, since the formed Al layer is thin, the process of making the Al-SiC composite is difficult due to the influence of the underlying Al-SiC composite.
SUMMARY OF THE INVENTION
The present invention has been made in view of such problems, and its object is to provide a metal matrix composite casting having a superior processability and a manufacturing method thereof.
In order to attain such an object, the metal matrix composite casting according to the present invention comprises a metal matrix composite, and a processed member inserted in the metal matrix composite by enveloped casting. By the processed member, a processed portion of a predetermined shape can be formed in the metal matrix composite.
That is, because the processed member is inserted in the metal matrix composite, by a simple processing such that the processed member is removed from the metal matrix composite, the processed portion having an approximately equal or similar shape with that of the processed member can be formed in the metal matrix composite. In this case, it is preferable to apply a mold release agent on the surface of the processed member. Due to this, the processed member can be removed from the metal matrix composite by a small force added thereto. As the mold release agent, carbon, boron nitride and so on can be used.
Alternatively, the processed member may be left in the metal matrix composite, and the processed portion may be formed in the processed member by a processing method such as cutting and drilling. In this case, the processed portion can be easily formed into a desired shape.
When the processed portion is formed in the processed member, it is desirable that the periphery of the processed portion is surrounded by the processed member. In this case, because the processability of the processed member is better than that of the metal matrix composite, the processed portion having a complicated shape such as a screw thread can be easily formed. Further, even if cracks occur in the processed member during formation of the screw thread, they do not reach the metal matrix composite. If the cracks are formed in the metal matrix composite, the metal matrix composite may break with the cracks becoming the starting points.
For example, a hole is formed as the processed portion. The hole can be used as a screw hole to which a bolt is fastened. The processed portion may taper away. Also, the surface of the processed portion may be flat or curved.
When the processed portion tapers away, by adding a force to the processed member from a taper-narrowing side of the processed portion to a taper-spreading side thereof, the processed member can be readily taken away from the processed portion.
Preferably, the difference in coefficient of thermal expansion between the processed member and the metal matrix composite is equal to or lower than 10×10
−6
/K. As a result, even though the metal matrix composite and the processed member inserted thereinto are exposed to temperature variation, the processed member can be prevented from separating from the metal matrix composite.
Alternatively, by increasing an interface strength between the processed member and the metal matrix composite also, high-quality metal matrix composite casting can be manufactured. To increase the interface strength, the processed member itself or the surface of the processed member is formed from a material which is easily wettable with the metal of the metal matrix composite. Or, by forming minute projections on the surface of the processed member, mechanical bonding strength between the processed member and the metal matrix composite may be increased.
Preferably, the processed member is formed from cast iron and the metal matrix composite is an Al-SiC composite. In this case, the difference in coefficient of thermal expansion between the processed member and the metal matrix composite becomes small. In addition to that combination, the processed member and the metal matrix composite as described later can be used.
The metal matrix composite is formed by mixing the characteristic improving material with the metal serving as a host material.
The metal in the metal matrix composite is preferably one of elements that infiltrates into the processed member under high temperature and high pressure due to die-casting. As a result, the processed member is inserted in the metal matrix composite by enveloped casting, and the strength of the processed portion can be enhanced. Aluminum, aluminum alloys, magnesium, magnesium alloys, copper, copper alloys, zinc and zinc alloys can be used as the metal of the metal matrix composite.
The characteristic improving material is mixed to improve the characteristics of the metal of the metal matrix composite. Therefore, depending on the characteristics of the metal to be improved, the property, composition, form of the characteristic improving material are changed. The characteristic improving material is in a form of particle, fiber, short fiber or whisker. Silicon carbide (Sic), carbon, aluminum nitride (AlN), aluminum oxide (Al
2
O
3
), beryllium oxide (BeO), copper, silicon nitride, diamond and the like can be used as the characteristic improving material.
When the molten metal is poured into the cavity of the casting mold filled. with the characteristic improving material, the metal with which the characteristic improving material has been mixed in advance can be poured into the cavity.
The metal matrix composite casting can be manufactured by the following method. That is, the method includes a step of disposing a processed member in a cavity of a casting mold, a step of filling the inside of the cavity with a characteristic improving material, a step of pouring metal into the cavity by pressure-casting, thereby forming a metal matrix composite composed of the characteristic improving material and the metal, and a step of forming a processed portion of a predetermined shape by using the processed member.
According to this method, the metal matrix composite is pressure-

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