Critical undercooling of growth mode transition in undercooled Al-80%Si-1.0%P alloy

Abstract

Herein, the critical undercooling of growth mode transitions in highly undercooled Al-80%Si-1.0%P alloys were investigated by high-speed video to observe and record the growth process. Under low undercooling, the dendrites with special edges of primary silicon solidify from the undercooled melt and show lateral growth characteristics. As undercooling increases, the primary silicon grows as blocky and dendritic shapes, indicating mixed growth characteristics. With sufficiently high undercooling, the sample’s surface exhibits the equiaxed primary silicon and shows non-lateral growth characteristics. The experimentally determined critical undercooling for the growth mode transition of primary silicon in undercooled Al-80%Si-1.0%P alloys are 125 and 225 K, and are consistent with the theoretically predicted values, 112 and 208 K, respectively.