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

Abstract

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 788K for 4h, 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 498K for 12h and the ultimate tensile strength, yield tensile strength and elongation were 293MPa, 175MPa 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 473K, 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.