Effect of Sr on the morphology of Si in unidirectionally solidified Al-Si alloy

The change in Si phase morphology at the solid/liquid interface by addition of Sr was observed using an improved unidirectional solidification method to investigate the mechanism of modification of Al-Si alloys. A self sealing method was used to prevent Sr from evaporating and oxidizing. Al-Si alloy was best aligned at a speed of 2mm/h and Sr addition worsened the degree of alignment. As the solidification rate decreased, the degree of interfacial smoothness also decreased in Al-Si-Sr alloy, while it increased in Al-Si alloy. Si phase protruded into the liquid phase in Al-Si-Sr alloy, although Si phase was covered by α phase in Al-Si alloy. That phenomenon was caused by the change in the balance between α phase/liquid interfacial energy and Si phase/liquid interfacial energy. The equilibrium condition was achieved by holding the furnace stationary for 5hours.