Refinement of Primary and Eutectic Silicon Particles in Hypereutectic Al-Si Alloys Using an Applied Electric Potential

Abstract

The effects of applied electric current on the cast microstructure of hypoeutectic Al-13 wt.% Si and Al-20 wt.% Si alloys have been investigated. This involved, with a constant voltage power supply, an application of an electric current density of about 500 mA/cm2 of melt surface area to laboratory-size ingots during solidification in a metal mold. In general, the applied electric current refined the cast microstructure of the hypereutectic Al-Si alloys. Specifically, the electric current did not modify the eutectic silicon particle, but changed the size distribution of the primary silicon particles by increasing the population of comparatively smaller size particles. The extent of the observed cast microstructure refinement was less than the reported effects of applied electric current in the technical literature and is significantly less than the effects of the traditional refinement obtained by addition of strontium and phosphorus to the molten metal prior to casting.