SI PHASE NUCLEATION ON SIC PARTICULATE REINFORCEMENT IN HYPEREUTECTICAL-SI ALLOY MATRIX

The solidification process of a hypereutectic Al-17wt.%Si-0.31wt.%Mg a lloy with 15 wt.%SiC particles was investigated by quenching samples t hrough the solidification region and by conventional casting of sample s from the mechanically stirred composite melts. The nucleation and gr owth processes of the primary Si phase under both stirred and unstirre d conditions were examined, and the Si/SiC(p) interface was analysed b y SEM and EDX with X-ray image analysis. The Si phase of Al-Si alloys has a more important role than the alpha phase in the bonding of the S iC reinforcement with the matrix, because the Si phase nucleates prefe rentially on the SiC particles even when the spinel interfacial layer exists. The crystal structures of the phases in the composites were id entified by X-ray diffraction, and the factors which influence the het erogeneous nucleation of Si crystal on the substrates are discussed.