Separation of aluminum and silicon from crystallizing Al–12.6wt%Si eutectic melts by applying an electromagnetic force during directional solidification

Abstract

Fine eutectic phases grow in a coupled mode from a quiescent liquid pool with a eutectic composition under a usual casting condition. The Al–12.6mass%Si (hereafter Al–12.6 %Si for simplicity) alloy belongs to such a typical eutectic system that consists of fine Si plates/rods embedding in the Al matrix after solidification. Conventionally, it seems impossible to separate Al and Si from the eutectic alloy in directional solidification. Herein, we developed a novel process to separate Al and Si from the eutectic liquid when a directional electromagnetic force (EMF) was applied upon the crystallizing solid/liquid interface. Solidification structures were observed, confirming that Al and Si could be effectively separated from the eutectic melt during continuous casting. Fluid flow simulation results were applied to elucidate the separation behavior and growth directions of Al dendrites and Si crystals. The formation mechanism of the Al dendrites as the leading phase was clarified when considering the turbulent fluid flow upon the application of EMF. The influence of the casting speed and Lorentz force on the separation efficiency was examined, which plays a key role in scaling up the casting billet for application in industry. The aggregated Si crystals were characterized by the electron backscatter diffraction (EBSD) technique, showing convincing evidence of Si growth, which is of importance in modifying the casting setup. The successful separation of Al and Si from the eutectic alloy using the present technique can eventually amend the recycling chain of Al–Si based alloys; casting Al scraps can be upgraded to wrought Al-based materials and the separated Si blocks can be reused to produce photovoltaic cells. Finally, an ideal setup was proposed for the continuous casting of Al and Si metals simultaneously as they can be separated effectively, which may serve as a raw model in tackling with the tough challenge of the eutectic alloy recycling.