Study of 6061-Al 2 O 3p composites produced by reciprocating extrusion
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I. INTRODUCTION
METAL matrix composites are well known for their attractive physical and mechanical properties, such as high specific modulus, strength, wear resistance, damping capacity, and thermal stability.[1–10] They have potential applications in aerospace, automotive, sports, and other structures. However, the realization of broad and extensive applications still requires a low cost and a high reliability in these products. Recently, particulate-reinforced Al matrix composites have received more attention than other metal matrix composites because of their low density and material cost. They are usually synthesized using powder metallurgy or methods involving molten metal. In the microstructural aspect, it has been well established that the spatial distribution of the reinforcement particles, porosity, and unwelded interparticle boundaries are very important for ductility and toughness, which in turn relates with reliability. Particle-clustering regions initiate damage cracks and provide favorable paths for the link-up of cracks.[11,12] Similar effects hold true for pores and unwelded interfaces. Thus, it is important to produce sound composites with a uniform spatial distribution of particles that is free of unwelded interfaces. Basically, the casting route involves segregation, pores, and oxide films in the as-cast structure, whereas the powder metallurgy route introduces particle clustering, interparticle HSU-SHEN CHU, Postdoctoral Candidate, and KUO-SHUNG LIU and JIEN-WEI YEH, Professors, are with the Department of Materials Science and Engineering, National Tsing Hua University, Hsinchu, 30043, Taiwan, Republic of China. Manuscript submitted October 13, 1998. METALLURGICAL AND MATERIALS TRANSACTIONS A
oxide layers, and contaminants in the as-pressed state. As a result, both routes often require subsequent hot or cold work to eliminate these defects and improve the properties of the end products. However, full elimination of defects requires a large amount of work, which normally reduces at least one of the product’s dimensions and limits their applications. Moreover, this brings a higher probability of the cracking or tearing of the workpieces during processing because of the high content of reinforced particles. In this study, a reciprocating extrusion process was developed to consolidate 6061Al/Al2O3p composites in a large accumulated deformation from mixing powders with an aim to eliminate the deleterious defects mentioned previously. This could solve the dimensional problem and cracking trouble at the same time. In addition to these advantages, the mechanical properties of the composites, including strength, modulus, ductility, wear resistance, and friction coefficient, were evaluated and discussed as a function of the volume fraction Al2O3. II. EXPERIMENTAL PROCEDURE A. Material Synthesis Two powders were used for making the experimental 6061Al/Al2O3p composites. The matrix was from the commercial air-atomized 6061 alloy powder. The chemical analysis of its composition (on a wt pct basis) is 0.98Mg
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