Abstract: In the process of preparing polycrystalline silicon using Al-Si alloy purification, the enrichment of primary silicon can effectively reduce the consumption of aluminum and acid in the subsequent pickling process, thereby lowering the separation cost of high-purity primary silicon. Electromagnetic directional solidification is one of the best methods for preparing polycrystalline silicon currently due to its advantages such as simple process and strong controllability. However, there is a lack of systematic research on how various process parameters affect the enrichment of primary silicon. Therefore, this study investigates the effects of initial solidification temperature, crucible initial position, and descent rate on the behavior of primary silicon enrichment during the solidification process of Al-50%Si (mass fraction) alloy, and characterizes the morphology of primary silicon grains within the enrichment zone. The results show that when the initial solidification temperature is 950 ℃, the initial crucible position is -5 mm, and the crucible descent rate is 2 mm/h, primary silicon is mainly concentrated in the lower part of the ingot with a maximum enrichment rate of 79.1%, which is the optimal combination of processes. At the same time, as the degree of primary silicon enrichment increases, the primary silicon grains change from “disk-like” to coarse “spherical”, which helps reduce the inclusion of primary silicon and improve its purity.

Key words: Al-Si alloy, electromagnetic directional solidification, primary silicon, silicon enrichment, temperature gradient, primary silicon morphology