Microstructure studies in SiC particle reinforced aluminium matrix composites processed by solidification route

Solidification structure of Al-Cu-SiCp and Al-Mg-SiCp composites solidified under different solidification rates have been studied. Al-Cu-SiCp composites solidified in large size permanent moulds exhibit conical-shaped particle-depleted zone in the bottom part of the casting. Columnar grains were observed in the particle depleted zone, while the particle-containing region exhibited equiaxed grain morphology. In the absence of convection, the presence of SiC particles promote matrix grain refinement. Matrix dendrite arm spacing (DAS) was not significantly altered by the presence of SiC particles. In the case of Al-Si-Mg-SiC composites, size of eutectic silicon and also its morphology changes from needle like to equiaxed. This is attributed to the heterogeneous nucleation of eutectic Si on SiC particles. Under all the solidification conditions studied in the present investigation, SiC particles are found to be rejected by the growing dendrites.