Mechanism of primary Si and Fe-segregation for a hypereutectic 90 wt.% Si–Ti alloy melt in directional solidification via electromagnetism

The electromagnetic directional solidification (DS) phase separation experiments of high silicon 90 wt.% Si–Ti alloy were performed under various pulling-down speeds. The results showed that Si enriched layer, Si + TiSi₂-rich layer and Si–Ti–Fe alloy layer appeared successively in axial direction of ingot after electromagnetic DS of 90 wt.% Si–Ti alloy melt at different pulling-down speeds. Separation of primary Si and segregation mechanism of metal impurities (Fe) during the electromagnetic DS process were controlled by pulling-down speed of ingot and electromagnetic stirring. When pulling-down speed was 5 μm/s, minimum thickness of the Si enriched layer was 29.4 mm, and the highest content of primary Si in this layer was 92.46 wt.%; meanwhile, the highest removal rate of Fe as metal impurity was 92.90%. The type of inclusions in the Si enriched layer is determined by Fe content of segregated Si enriched layer. When the pulling-down speed was 5 μm/s, the inclusions in the Si enriched layer were TiSi₂. Finally, when the pulling-down speed reached greater than 5 μm/s, the inclusions in the Si enriched layer evolved into TiSi₂ + τ₅.