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The 6061 Al-10 vol% SiC w composites were prepared by powder metallurgy with the powders having the different sizes, i.e. < 30 µm and 30 µm <. The composites were subjected to equal channel angular pressing (ECAP) under various conditions and the microstuctural changes during ECAP were examined. A special focus was made on the effect of ECAP conditions on the distribution of SiC whiskers. The present investigation was aimed at exploring the feasibility of ECAP as a post working process for manufacturing the discontinuous metal matrix composites. The microstructural examination and the microhardness measurement of the ECAPed samples suggested that the optimum combination of the uniform microstructure and enhanced mechanical properties would be obtained by (a) using the powders having the smaller size, (b) decreasing ECAP temperature, and (c) repeating ECAP.

The Mg chips were recycled using powder metallurgy method and was also reinforced with SiC particles of Vf 10%. The mechanical characteristics of recycled Mg and SiCp/Mg composite were investigated by microhardness and tensile tests, and were compared with those of cast Mg. The microhardness and tensile strength of recycled Mg produced with chips of 40 mm in average size were higher than those of cast Mg, and SiCp/Mg revealed much higher microhardness and tensile strength. The tensile strength of recycled Mg with fine chips of 40 mm was superior to that of recycled Mg with larger chips of 90 mm at room temperature. The tensile strengths of recycled Mg and SiCp/Mg lowered remarkably with increasing temperature. However, the tensile strength of recycled Mg was about two times larger than that of the cast Mg at 573 K. The recycled Mg revealed elongation of approximately less than 5% at room temperature, and the elongation decreased at temperatures higher than 473K.

Age hardening behaviors of SiC whisker reinforced composites with 6061 A1 matrix fabricated by P.M. (powder metallurgy) and squeeze casting were investigated to examine the effect of the fabrication method on the aging kinetics. In the squeeze cast composite, numorous triangular particles which is believed to be MgAI20~ were observed at AI/SiC interfaces whereas no visible interface particles were observed in the P. M. composite. P.M. composite showed faster age hardening and reached the maximum hardness earler than the squeeze cast composites. The decrease of the aging kinetics in squeeze cast 6061 AI matrix composites compared to that in P.M. composites is thought to result from more severe depletion of Mg atoms due to interfacial reactions in squeeze cast composites. The uniformity of whisker distribution is suggested to influence the general aging behavior through its effect on the local dislocation density. Data on the aging kinetics and the inteffacial reactions in other A1 alloys were also examined to study various factors which can influence the aging kinetics.