The solid/liquid phase transformation of ZL201 aluminium alloy in near liquidus semi-continuous casting was simulated using multiscale simulation technique. The models of temperature fields and phase transformation were established with respect to the continuous casting process. The solid fraction was used to couple the model between on macro-scale and on mesoscale. The steady state temperature fields of ZL201 alloys were calculated using the extrapolated non-physical boundary proposed in this paper. The average undercooling of the cells in transition region was used to calculate the nucleation rate in the melt with the help of Rappaz’s model. The microstructural evolutions were simulated for ZL201 alloys poured at near liquidus with the casting velocity 1.5

1

0 mm/s. It is shown that the casting velocity has large influence on the microstructure of semisolid alloy. Ideal grain size and distribution can be obtained when the casting velocity is in the range 2.0%

2

.5%.