Formation of the solidified microstructure in Mg–Sn binary alloy

The solidified microstructures in Mg–3Sn and Mg–5Sn (wt%) alloys were investigated experimentally. For Mg–3Sn, secondary and ternary dendrite arms grow rapidly from α-Mg equiaxed dendrites in a certain direction. When Sn content is increased to 5%, developed secondary and ternary dendrite arms in the upstream direction in the center of the sample do not occur. Formation of this microstructure characteristic was discussed in terms of cooling rate, force caused by fluid flow, and dendrite growth behavior of Mg–Sn alloy. The model for growth restriction factor (GRF) has been further discussed by considering the growth behavior of a dendrite tip, which reveals the relationship between GRF and dendrite growth rate. The relationship between GRF and constitutional undercooling was discussed during dendrite growth. The deviation of growth direction from <1 0 1¯ 0> crystal direction has been analyzed by fluid flow during solidification.