Solidification of the Undercooled Al-Si Alloy Containing 1.0 PctRE

Al-80 pctSi-1.0 pctRE alloy was levitated and melted using the electromagnetic levitation facility in combination with a laser heating unit. The growth morphologies of primary silicon were observed using a high-speed video, and the microstructure was analyzed by the scanning electron microscopy. The morphologies of primary silicon at low, intermediate, and high undercooling are dendrites, fragmented bulks and granular grains, and equiaxed grains, respectively. In addition, the growth velocities of primary silicon were measured, which were consistent with the theoretical prediction. The microstructure refinements of primary silicon played a dominant role in its large microhardness, which increased with the increase of undercooling. Moreover, the hardening effect of dendritic structure was stronger than that of equiaxed grain.