Comparison of the mechanical properties of A356-SiC particle-reinforced metal matrix composites produced by two melting routes

Abstract

SiC particle-reinforced metal matrix composites (MMCs) were produced by a common liquid-phase technique in two different melting routes. In the first route, 5, 10, 15 and 20 vol % SiC-reinforced A356-based MMCs were produced. In the second route, an Alcan A356 + 20 vol % SiC composite billet was diluted to obtain 5, 10, 15 and 20 vol % SiC-reinforced MMCs. In both cases the average particle size was 12 μ. The microstructural and mechanical property relationships of these composites were investigated. Vortex-produced MMCs showed a fairly good particle distribution accompanied by approximately 5-8 vol % porosity. Diluted Alcan composites produced excellent particle distribution and finer eutectic silicon crystals. Compressive and tensile properties were compared between vortex-produced and diluted composites. The results showed that diluted MMCs showed better properties compared with composites produced by the vortex method. Both composite groups were subjected to a T6 ageing heat treatment. The rate of increase in the yield, and tensile and compressive strength values were always higher in the as-cast materials than in T6 heat-treated composites with increasing SiC particle content. This difference was attributed to accelerated nucleation of precipitation and, therefore, overageing caused by ceramic particles. SEM investigations on the fracture surfaces showed that good particle bonding existed in the diluted composites.