Effect of Mixed Rare Earth and Strontium on Eutectic Silicon Morphology of Al-24%Si Alloy

The effects of mixed rare earth(RE), strontium and their composite modifier on eutectic silicon morphology of Al-24%Si alloy were studied with optical microscopy and SEM. The results show that the eutectic silicon in the alloy without modification treatment was coarse block-shape, loose arrangement and uneven. After it was modified by mixed RE, the shape of the eutectic silicon near primary silicon was fine particulate, whereas that far away from primary silicon was rod. The shape of the eutectic silicon after modified by Sr was short rod with secondary or tertiary branches. The morphology of eutectic silicon treated by composite modifier was smooth round-pole shape, its size was larger than that of treated by RE, and its amount was less than that of treated by Sr.