Effect of retrograde solubility on the purification of MG Si during fractional melting

MG Si can be effectively refined using a fractional melting process. The efficiency of fractional melting depends on two parameters, the heating rate and the wetness. Generally, the heating rate should be slow to ensure impurity diffusion and, in order to perfectly separate the liquid from the solid/liquid mixture, there should not be higher wetness. Many MG Si metal impurities exhibit retrograde solubility. The metal impurity behaviors with retrograde solubility were studied during the FM process. The change of the microstructure during the process was also studied with a SEM and an EPMA. Due to the retrograde behavior, slow heating below the maximum solubility temperature was not necessary to refine MG Si. For the FM process, the operating temperature range to refine MG Si should be carefully selected considering the behavior of major metal impurities in the mushy zone.