Silicon Particle Precipitation during DC Casting of Al-Si Clad Alloys

The formation of polyhedral silicon crystals in aluminium 7-9% silicon alloys has been studied both in industrial ingots and in simulation experiments in a Bridgman furnace. It was found that the nucleation temperature and the cooling rate were important factors influencing the amount and size of the polyhedral crystals. To avoid large particles in the as cast material early nucleation have to be suppressed and the phosphorous content should be kept low. Modelling of diffusion-controlled growth of the silicon phase in this type of aluminium-silicon alloys shows how the nucleation temperature influences the morphology of the precipitated sili¬con.