Grain refinement of primary silicon in hypereutectic Al-Si alloys by different P-containing compounds

The grain refinement behavior of Si-3P, Si-25Mn-10P, and Al-10Si-2Fe-3P master alloys on hypereutectic Al-24Si alloy was studied. Microstructure analysis indicates that the P-containing compounds in the three master alloys are SiP, MnP, and AlP, respectively. The coarse flower-like primary silicon in the Al-24Si alloy transforms into smaller, well-distributed blocks with the addition of various master alloys. When pouring at 840 °C, the average grain size of the primary silicon refined by Si-25Mn-10P master alloy with a holding time of 30 min is about 18 µm, which is significantly smaller than those refined by Si-3P and Al-10Si-2Fe-3P master alloys. The grain size shows an increasing trend when the holding time is further prolonged. Higher holding temperature has a positive effect on the grain refinement of Si-25Mn-10P master alloy. The grain refinement mechanism of the three master alloys was also discussed.