Modification Mechanism of Rare Earth La in Al-Si Alloy
Al-17Si-xLa alloys containing different contents of La (x=0, 0.3, 1,3, 6wt%) were prepared with cast metallurgy processing. By means of optical microscopy (OM), scanning electron microscopy (SEM) and electron probe microanalysis (EPMA), the effect of La on microstructure of hypereutectic Al-Si alloys was investigated, the morphology and composition of La-rich phases were also analyzed, and the modification mechanism of La in Al-Si alloy was discussed. The results show that rare earth La has a modification effect on the Si phases in binary hypereutectic Al-Si alloys, but it has a better modification effect on eutectic Si than on primary Si phase. The optimum modification effect can be obtained with 3wt.% La addition, La are enriched in the front of Si/Al interface, hence suppressing the growth of Si.