Microstructure and mechanical properties of low-pressure die casting Mg-10Gd-3Y-0.7Zr alloy

Mg-10Gd-3Y-0.7Zr alloy was prepared by low-pressure casting. Microstructure evolution of Mg-10Gd-3Y-0.7Zr alloy was observed by optical microscope, scanning electron microscope energy dis-fussion spectrometer and differential thermal analysis. The heat treatment process was optimized to improve the mechanical properties of the alloy, and strengthening mechanism of heat treatment on properties of the alloy was described based on microstructure analysis. The results indicate that the as-cast microstructure of Mg-10Gd-3Y-0.7Zr alloy is composed of primary α-Mg and eutectic Mg₂₄ (Gd, Y)₅ phase which is distributed coherently along the grain boundary. After heat treatment, the continuous distributed Mg₂₄ (Gd, Y)₅ phase disappears, and primary α-Mg and Mg₅ (Gd, Y) particles exist mainly in the alloy. Under 520℃ × 14 h + 230℃ × 20 h treatment conditions, the desirable mechanical properties can be obtained. After solution heat treatment at 520℃ for 4 h, the strength of Mg-10Gd-3Y-0.7Zr alloy exhibits neglected change, while the elongation is increased from 5.5% to 13.4%, increased by 144%. After aging at 230℃, the mechanical properties of Mg-10Gd-3Y-0.7Zr alloy exhibit excellent, where the tensile strength, yield strength and elongation reach 307.8 MPa, 200.4 MPa and 7.2%, respectively, increased by 41%, 38% and 31% compared with those of the as-cast sample.