Effect of strontium on columnar growth of dendriticαphase
in near-eutectic Al-11.6%Si alloys①
in near-eutectic Al-11.6%Si alloys①
(1. Department of Mechanical Engineering, Southeast University, Nanjing 210018, China;
2. College of Materials, Nanjing University of Technology, Nanjing 210009, China)
2. College of Materials, Nanjing University of Technology, Nanjing 210009, China)
Abstract: For Al-11.6%Si alloy, the influence of the addition of Sr on the morphology of the dendriteαphase was investigated, and the characteristic parameters of the dendriteαphase, the primary dendrite spacing and the secondary dendrite arm spacing, were also measured. The addition of strontium promotes the columnar dendrite growth and leads to a decrease of both the primary dendrite spacing and secondary dendrite arm spacing with the increase of the content of strontium 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 dendriteαphase, consequently resulting in a decrease of the growth undercooling of dendrite tips. And hence, the nucleation of the equiaxed grains in the liquid in front of the columnar dendrite tips is restrained, thus the addition of strontium in Al-Si alloys promotes the growth of the columnar dendrites. The reduction of the solid-liquid interfacial energy also leads to the decreases in the primary dendrite spacing and the secondary dendrite arm spacing.
Key words: Al-Si alloy; primary dendrite spacing; secondary dendrite arm spacing; strontium; microstructure