The relevance of melt convection to grain refinement in Al-Si alloys solidified under the impact of electric currents

This paper considers the directional solidification of Al-7 wt.% Si alloys under the influence of strong electric currents for the configuration of two parallel electrodes immersed from the free surface into the solidifying alloy. Solidification experiments were performed under the influence of both direct currents (DC) and rectangular electric current pulses (ECP). The interaction between the applied current and its own induced magnetic field causes a Lorentz force, which produces an electro-vortex flow covering the entire melt area. Numerical simulations of the magnetohydrodynamic problem were conducted to calculate the Lorentz force, Joule heating and induced melt flow. The numerical predictions were confirmed by isothermal flow measurements in eutectic Ga-20 wt.% In-12 wt.% Sn. The application of the electric current during solidification leads to the formation of refined equiaxed grain structures. There are no remarkable differences with respect to the influence of DC or ECP treatment on the mean grain size and the area of equiaxed zone in the solidified samples, provided the effective values of the current strength are identical. The results demonstrate that the grain refining effect observed in these experiments can be ascribed solely to the forced melt flow driven by the Lorentz force. (C) 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.