Refinement of Primary Si Phase in Hypereutectic Al–Si Alloy by Electrically Assisted Solidification with P Addition

The efficient processing of hypereutectic Al–Si alloys depends on controlling the microstructure of the primary Si phase during solidification. This study investigates the effects of electric current and phosphorus (P) addition on the refinement of primary Si, with the results confirming that applying electric current during solidification refines the primary Si phase; introducing P further enhances this refinement. Notably, when 10 ppm of P is added (below the identified critical amount of 20 ppm), an improved refinement effect is observed compared with the application of either electric current or P alone. Applying an electric current generates a circulating flow within the melt, resulting in an increased cooling rate, which leads to improved nucleation behavior for the primary Si phase. In addition, the circulating flow generated within the melt influences the dispersion of aluminum phosphide during nucleation. Adding P at concentrations above 40 ppm does not yield further benefits, suggesting a saturation point for its efficacy. This study demonstrates that the concurrent electric current application and minimal P addition can significantly enhance the refinement of primary Si phases, offering a potent approach for optimizing the microstructural properties of hypereutectic Al–Si alloys.