Fine-grained structural materials（FSM for short）with the same composition of Al-18Si alloy were used as the master alloy to modify the microstructure of HCC Al-18Si alloys because of its structural heredity.The influences of FSM master alloy on the microstructure and uniformity of Al-18Si alloy were investigated by SEM（scanning electron microscopy）and DSC.The results show that FSM master alloy can reduce the size of primary Si and improve the uniformity of the billet along the cross-section.The addition of FSM master alloy can increase the nucleation temperature of primary Si and reduce the latent heat of crystallization.In addition

with the addition of the master alloy

the alloys is less sensitive to cooling rate by DSC analysis

which reveals that the differences of nucleation temperature at surface and center of the billet is decreased.