Effect of Si content on separation and purification of the primary Si phase from hypereutectic Al-Si alloy using rotating magnetic field

Effect of Si content on separation and purification of the primary Si phase from hypereutectic Al-Si alloy using rotating magnetic field (RMF) was investigated in the present study. The results showed that the Si content has an obvious influence on the thickness of Si-rich layer formed around the sample and impurity contents in the purified Si. The thickness of Si-rich layer increases and the Si content in the Si-rich layer decreases with increasing Si content of the hypereutectic Al-Si alloy. The impurity contents of the purified Si can be reduced to a very low level. The typical metallic impurities (Fe, Ti, and Ca) have a high removal fraction. Electron probe microanalyzer (EPMA) analysis clearly reveals that the B content is lower in the primary Si phase than that in the Al-Si eutectic, suggesting the segregation of B element between the primary Si phase and the remaining liquid during solidification. In addition, the contents of B and metallic impurities (Fe, Ti and Ca) increase with increasing Si content of the Al-Si melt due to the segregation process starting at higher temperatures with higher Si content.