Effects of heat treatments on microstructures and mechanical properties of Mg–4Y–2.5Nd–0.7Zr alloy

A systematic study was carried out to elevate the strength of Mg–4Y–2.5Nd–0.7Zr (wt%) alloy by optimized heat treatment parameters. Microstructures and mechanical properties of this tested alloy in the as-cast, solution-treated and different ageing conditions were investigated. After solution treatment at 788 K for 4 h, the eutectic compounds Mg41Nd5 and β phase dissolved into the matrix. A satisfied combination of high tensile strength and ductility was obtained when the alloy was aged at 498 K for 12 h and the ultimate tensile strength, yield tensile strength and elongation were 293 MPa, 175 MPa and 5.6%, respectively. The superior strength was mainly attributed to the fine dispersed β″ phase and β' phase which coexisted together in the peak-aged stage. Prolonging the ageing time to the over-aged state or increasing the ageing temperature, the strength could be weakened by the coarse β' phase. Peak-aged at a relatively low temperature of 473 K, the dominant fine strengthening β″ phase with DO19 structure led to a strength decline. According to strengthening contribution calculation, it revealed that both solid solution strengthening and precipitation strengthening play an important role in improving the strength.