Evolution of primary phase in solidification of Al-Si alloys

Abstract

The morphology of primary phase in solidification of hypo-eutectic Al-Si alloys has been investigated by both experiment and numerical simulation using the modified cellular automaton(MCA) method. In order to generate the globular structure without any thermo-mechanical stirring, the effects of pouring temperature, cooling rate and inoculation on the evolution of globular structure were examined. The optimum condition for obtaining uniform and fine globular structure is that the pouring temperature should be as closely low as to the liquidus and the cooling rate should be less than 0.3°C/sec. As the pouring temperature and the cooling rate increase, the primary phase transforms from globular to rosette-like, and finally to dendritic structure. The inoculation with nucleation potency is also very effective in forming a globular structure. The dominant mechanism responsible for the evolution of globular structure was found to be the increase of nucleation sites due to the lower pouring temperature, inoculation, and uniform solute distribution due to the lower cooling rate.