SILICON CRYSTAL FORMATION DURING DC CASTING OF ALUMINIUM-SILICON ALLOYS

The formation of polyhedral silicon crystals in aluminium 7-8% silicon alloys has been studied in industrial ingots. 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. Modeling of diffusion-controlled growth of the silicon phase in this type of aluminium-silicon alloys shows how die nucleation temperature influences the morphology of the precipitated silicon.