Effect of strontium on columnar growth of dendritic α phase in near-eute ctic Al-11.6%Si alloys

For Al-11.6%Si alloy,the influence of the addition of Sr on the morphology of the dendrite α phase was investigated,and the characteristic parameters of the dendrite α phase,the primary dendrite spacing and the secondary dendr ite arm spacing,were also measured. The addition of strontium promotes the colu mnar dendrite growth and leads to a decrease of both the primary dendrite spacin g and secondary dendrite arm spacing with the increase of the content of stronti um in the modified near-eutectic Al-Si alloys. It is thought that the addition of Sr leads to a reduction of the solid-liquid interfacial energy of the dendr ite α phase,consequently resulting in a decrease of the growth undercoolin g of dendrite tips. And hence,the nucleation of the equiaxed grains in the liqu id in front of the columnar dendrite tips is restrained,thus the addition of st rontium in Al-Si alloys promotes the growth of the columnar dendrites. The redu ction of the solid-liquid interfacial energy also leads to the decreases in the primary dendrite spacing and the secondary dendrite arm spacing.