Effect of Sr on the microstructure and mechanical properties of hypereutectic Al-Si alloy

The hypereutectic aluminum silicon alloy (Si: 20wt.%) was modified by Al-10%Sr modifier. The results show that Sr has a significant refining effect on both primary and eutectic silicon in aluminum silicon alloy (Si: 20wt.%). When the additional amount of Sr reaches 0.4%, the grain size is refined from 80-100 μm without modification to 30-50 μm after modification. The morphology of primary silicon has changed from a large plate-like shape to a deformed fine fishbone shape, while eutectic silicon has changed from a long needle shape to a point shape. The X-ray diffraction analysis results indicate that the Al₂Si₂Sr phase was generated in the modified alloy. The scanning electron microscopy analysis results show that after 0.4% Sr modification, a white triangular-shaped Al₂Si₂Sr phase appears in the aluminum silicon alloy (Si: 20wt.%) sample, which is the Al-Si-Sr ternary phase analyzed by XRD testing. The tensile testing results show that the Sr modification additional amount is 0.4%, and the tensile strength of aluminum silicon alloy (Si: 20wt.%) has been improved by about 11% from 162 MPa without modification to 200 MPa after modification.