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MATERIALS RESEARCH

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Low volume fraction SiCpy AA 380.0 composites fabricated by vacuum infiltration Wen-Sheng Chung, Shou-Yi Chang, and Su-Jien Lin Department of Materials Science and Engineering, National Tsing Hua University, Hsinchu, Taiwan, Republic of China (Received 30 January 1997; accepted 20 July 1998)

A vacuum infiltration process has been developed to fabricate the aluminum matrix composites reinforced with low volume fraction (,50 vol%) of SiCp . Generally, it is difficult to fabricate low volume fraction particulate composites by traditional infiltration processes because the particles always pack up to about 50 vol% in the preforms or compacts. In this study, the powder compacts were prepared of the well-mixed Ni-coated SiCp and pure aluminum powders and then were packed in quartz tubes. An aluminum alloy (Al –8.7% Si–2.6% Cu) with a composition similar to AA 380.0 was used to infiltrate these compacts. Experimental results showed that the infiltration temperature of 640 ±C is favorable for the fabrication of these composites. Infiltration behavior, microstructure, nickel distribution, bending test, and fractography of the composites were investigated.

I. INTRODUCTION

Infiltration processes have been mentioned in several studies1–10 for the fabrication of metal matrix composites (MMC’s), especially for the metallic matrix with a low melting point such as aluminum alloy. Infiltration processes can be applied to fabricate the composites containing any kinds of reinforcements, including particles,1– 6 whiskers,7 short fibers,8,9 and continuous fibers.10 Among composites, particle reinforcement is very popular. Preparation of the powder preforms or compacts is a necessary procedure before the infiltration. However, the mono-size particulate reinforcements typically pack up to about 50 vol% in the preforms or compacts,11 resulting in the volume fraction of reinforcements in the infiltrated composites being limited to about 50 vol%. Unfortunately, the typical volume fractions of the particulate reinforcements in the composites are about 10–30 vol% for most applications. For the fabrication of the composites containing a low volume fraction of reinforcements, traditional powder metallurgy12 and casting13,14 techniques have been used. The powder metallurgy process is costly and the casting process usually yields some unexpected defects. Accordingly, a special infiltration process for fabricating the low volume fraction particulate composites is an interesting subject from viewpoints of the application and process development of composites. The purpose of this study is to develop an infiltration process for the fabrication of aluminum matrix composites reinforced with low volume fraction (less than 50 vol%) of particulate reinforcements. The nickel film was coated on SiCp to improve the wettability to the molten aluminum alloy. Various amounts of pure J. Mater. Res., Vol. 14, No. 3, Mar 1999

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aluminum powders were mixed with th