Effects of Ultrasonic Treatment on the Microstructure and Mechanical Properties of Mg-3Y-3.5Sm-2Zn-0.6Zr (wt %) Alloy

Ultrasonic treatment (UST) was applied in the smelting process of Mg-3Y-3.5Sm-2Zn-0.6Zr (wt %) alloy and the microstructure as well as mechanical properties of the experimental alloy were investigated. Results showed that the effect of UST on grain refinement was obvious, and the distribution of the second phases along grain boundary became discontinuous. The width of the grain boundary precipitates decreased after UST. The contents of solute elements within grains increased, and the morphologies of Zr-rich compounds and Y-rich compounds both at grain boundaries and within grains changed after UST. The mechanical properties of the experimental alloy after UST were significantly improved. The ultimate tensile strength (UTS) was 265 MPa, the tensile yield strength (TYS) was 171 MPa, and the elongation (EL) was 11%. The mechanism of UST of the alloy can be attributed to the combined effects of cavitation-induced heterogeneous nucleation and melt convection induced by acoustic streaming, resulting in the refinement of grains and the grain boundary precipitates, which promoted the improvement of mechanical properties.