High cycle fatigue behavior and mechanical performance of a novel sand-cast Mg-Nd-Gd alloy: Effect of heat treatment

This work was primarily aimed at evaluating the effect of heat treatment on the microstructure, high cycle fatigue behavior and mechanical properties of a novel sand-cast Mg-3Nd-2.6Gd-0.2Zn-0.5Zr alloy. Results indicated that the as-cast studied alloy consisted of non-dendritic α-Mg grains and considerable eutectic phases distributed along grain boundaries, most of which could been successfully dissolved into matrix accompanied by the appearance of rod-shaped Zn–Zr phases after subjected to the optimized solution treatment (535 °C × 10 h). Examinations of microstructure revealed a finely dense dispersion of predominant β′′ and minor β′ phases in the peak-aged studied alloy (isothermally aging at 200 °C for 14 h). Tensile properties were significantly improved, and the relatively best combination of strength and ductility was obtained in peak-aged condition (YS = 220 MPa, UTS = 303 MPa and EL = 4.1%). Heat treatment conditions were found to exert a pronounced influence on the high cycle fatigue properties, and the highest fatigue strength σf (approximately 121.5 MPa), was achieved in peak-aged studied alloy, which is about 24% higher than that of commercial NZ30K-T6 alloy. Owing to the specifically significant response to heat treatments, the fatigue strength of the studied alloy was confirmed to increase in a near linear relationship with the increasing yield strength and ultimate tensile strength. This is also well consistent with the characteristic fatigue life predicted by Weibull statistics in different heat treatment conditions.