Effect of Sn addition on the separation and purification of primary Si from solidification of Al-30Si melt under electromagnetic stirring

Abstract

In the present work, the effect of Sn addition on the separation and purification of primary Si from solidification of Al-30Si melt under rotating magnetic field (RMF) was investigated. The results revealed that the as-cast solidification microstructure of ternary Al-30Si-Sn alloy is composed of the primary Si phase, eutectic α-Al+Si, and eutectic α-Al+β-Sn structure. The application of RMF can separate the primary Si from solidification of Al-30Si-Sn melt, consequently forming a Si-rich layer on the periphery of the ingot. The atomic fraction of primary Si in Si-rich layer increases with increasing Sn content because the addition of Sn can enlarge the crystallization temperature range of the primary Si phase. The content of non-metallic B in primary Si increases due to the increasing segregation coefficient of B with the increasing Sn content. However, the contents of typical metallic impurities (Fe and Ca) exhibit an opposite trend, which may be attributed to the back-diffusion of impurities suppressed by the addition of Sn.