Abstract: Effect of mixed addition of light and heavy rare earth elements (La, Ce, Gd, Ho, Er) on the microstructure and mechanical properties of Al-6.9Si-0.36Mg alloy was studied by using optical microscope, scanning electron microscope/energy dispersive spectroscopy, and mechanical property testers. The results show that the refinement effect of α-Al grains in the as-cast alloy is significant with total rare earth addition of 0.1%. As total amount of rare earth added is 0.4%, the improvement effect on the eutectic Si phase is significant, and the eutectic Si phase changes from coarse needle-shaped to granular. After T6 heat treatment, the eutectic Si phase further transforms into small particles and uniformly distribute in the matrix, reducing the cutting effect on the matrix. When the total amount of rare earth elements added is 0.4%, the mechanical properties of the T6 heat treated alloy are the best with tensile strength of 285.4 MPa, elongation after fracture of 7.0%, and hardness of 89.2 HBW.

Key words: rare earth, Al-Si-Mg alloy, microstructure, mechanical properties