Refinement of Primary Silicon Crystals by Novel P-doped γ-Al_2O_3 Particles in Solidification of Hypereutectic Al-Si Alloys

摘要

P-doped γ-Al_2O_3 was found to be a potent substrate to nucleate primary silicon whilst good modification of the eutectic matrix is retained during solidification of hypereutectic Al-Si alloys. On using P-doped γ-Al_2O_3 could be a perfect and clean source of P without additional impurities. The optical micrographs show that the morphologies of primary silicon crystals in solidification of Al-18Si alloy are changed from irregular coarse morphologies to fine regular particles. The average particle size of primary Si decreased from 52 μm to 25 μm and 22 μm in adding P-doped α-Al_2O_3 and P-doped γ-Al_2O_3 respectively. It was clear that P-doped γ-Al_2O_3 led to good refinement of primary Si and the modification effect on eutectic Si was retained in solidification of commercial purity Al-18Si alloy. Adding P-doped γ-Al_2O_3 give a good primary Si refinement to Al-18Si alloy if compared with the addition of P and using finer P doped γ-Al_2O_3 powder give narrower particle size range similar to that of adding P.