Abstract:The modification effects of La addition on the microstructural evolution of hypereutectic Al-17% Si and Al-25% Si(mass fraction) alloys were investigated. The Al-Si alloys were fabricated using conventional casting, spray atomization and deposition processing. Microstructures were examined using optical microscopy and SEM. The results show that the addition of La has strong modification effect on the conventional microstructure of as-cast Al-Si alloys, while little effect on that of spray-deposited Al-Si alloys. EDS and XRD experiments show that La reacts with Al and Si to form some intermetallics, which can be represented as AlSi₂La₂ consisting of LaSi₂ and some unknown ternary AlSi_xLa_y phase. Spray atomization and deposition processing show significant microstructural modification in Al-17Si-xLa alloys as compared to their as-cast counterpart. Equiaxed Si particulates were observed evenly distributed in all the spray-deposited Al-17Si-xLa alloys regardless of the addition of La.

Key words:  hypereutectic Al-Si alloy; casting; spray atomization and deposition; modification