Separation mechanism of the primary Si phase from the hypereutectic Al-Si alloy using a rotating magnetic field during solidification

Understanding solidification behavior under an intense flow field is important in controlling the microstructure and macrostructure of alloys in industry. In the present study, we show that using a rotating magnetic field (RMF) during solidification of hypereutectic Al-Si alloy can efficiently congregate the primary Si phase to the inner wall of the crucible and form a Si-rich layer with 65-698 wt.% Si content. The Al-Si melt flow under an RMF and the temperature field of the liquid metal are the two dominant conditions for the segregation of the primary Si phase. The intense melt flow, i.e., secondary flow and Taylor-Görtler vortices, carries the bulk liquid with higher Si content to promote the growth of the primary Si phase formed close to the inner wall of the crucible where the temperature is low, finally resulting in the remarkable segregation of the primary Si phase. This work has demonstrated that a forced intense melt flow combined with proper cooling conditions can greatly change the solidification structure of alloys, which is beneficial to microstructure control.