Effects of neodymium addition on microstructure and mechanical properties of near-eutectic Al-12Si alloys

The microstructure and mechanical properties of near-eutectic Al-12Si alloys modified with 0-0.4% Nd (mass fraction) were investigated. The results indicate that a submicro- or nano-sized Al2Nd phase is observed in the modified alloy with 0.3% Nd. The morphology of the α(Al) phase is significantly refined in the Nd-modified alloys. The primary Si morphology simultaneously changes into a fine, particle-like morphology, and the morphology of eutectic Si becomes fine-fibrous instead of coarse-acicular. Relatively few growth twins are observed on the surface of the Si plate in the Al-12Si-0.3Nd alloy at the optimal modification level. The mechanical property test results confirm that the mechanical properties of the as-cast Al-12Si alloys are enhanced after the Nd addition, with optimal ultimate tensile strength (UTS) of 252 MPa and elongation (EL) of 13% at an Nd content of 0.3%. The improved mechanical properties are attributed to the refined morphology of Si phase and the formation of the Al2Nd phase.