Effect of cavity shape on microstructural evolution of pure aluminum in electrically-assisted solidification.

Grain refinement is a crucial issue in metallic materials. One of the emerging techniques to obtain equiaxed grains is to apply an electric current to the liquid metal during solidification. With this view, in this paper, the effect of electric current on the solidification behavior in various cavity shapes of mold was investigated. Cylinder-, cube-, and cuboid-shaped cavities designed to have similar cavity volume were used. By applying an electric current during the solidification of liquid aluminum, the grains were effectively refined with a grain size of approximately 350 µm for all three types of cavities. The circulating flow of liquid aluminum was observed to have a similar shear rate intensity in all three types of cavities, which is known to be sufficiently high (over hundreds of s) to induce dendrite fragmentation resulting newly generated nuclei. Dispersion of nuclei on unsolidified aluminum appeared differently according to the shape of the cavity, which influences final shape of refined zone. The area fraction of refined zone was affected by the relative relationship between the solidification completion time and the electric current application time. This study will provide insight to control of process parameters when electrically-assisted solidification is applied to a real product with a complex shape.