Effect of chilling on the microstructure during directional solidification, of A356-SiC composite

Microstructures of aluminum silicon alloy A356 containing 0-20 vol. % SiC particles formed during directional solidification from a chill have been studied and compared with the structures of the base alloy under similar mould conditions. Columnar dendritic structure was observed during solidification of the base alloy at different locations from the chill mould surface. In the case of composites, the presence of silicon carbide particles disturb the orderly aligned arrangement of the dendritic observed in the base alloy under similar solidification conditions, except near the chill surface where a particle-free zone is observed due to pushing of particles by the macroscopic solidification front with cell spacing finer than the particle size. Solidification conditions e.g., cooling rate and temperature gradient and rate of advancement of the solidification is studied in this work. The study indicates that the presence of particles themselves alter the cooling rates, temperature gradients and growth rate of macroscopic solidification under identical thermal conditions during solidification. The possible influence of these alterations in growth condition on the solidification microstructure due to the presence of particles are discussed together with the other possible direct influences of particles on dendritic growth of aluminum silicon alloys. (author)