THE INFLUENCE OF Cu ON EUTECTIC NUCLEATION AND MORPHOLOGY IN HYPOEUTECTIC Al-Si ALLOYS

The influence of increasing additions of copper on the aluminium silicon eutectic nucleation and morphology was investigated in unmodified and Sr-modified Al-10wt% Si alloys. In unmodified alloys, increase in copper content resulted in an increase in the number of polyhedral silicon particles and thus nucleation frequency of eutectic cells. In Sr modified alloys, additions of copper resulted in an increase in the nucleation frequency of eutectic cells. Also, at high copper levels in modified alloys, a change in the eutectic interface morphology from near-planar to coral-like was observed. These observations contribute to new insight in the solidification path and morphological evolution of Al-Si eutectics, and serve to provide in-situ X-radiography observations of eutectic solidification in Al-Si alloys with a more general validity.