Fatigue behavior of as-cast and T6-treated Mg–9Al-0.4Zn-1.5Sn alloy at RT and 150 °C

This study systematically investigates the effects of heat treatment on the fatigue behavior of Mg-9Al-0.4Zn-1.5Sn alloy under both room temperature and an elevated temperature of 150 °C. Fatigue cracks mainly nucleate at casting defects (porosity, shrinkage cavities, old oxides) and surface grains. At the elevated temperature, oxidation accelerates at crack tips under cyclic loading, where brittle oxides act as stress concentrators and secondary initiation sites, promoting crack branching and growth. Fine precipitates, residual phases at grain boundaries, and Mg 2 Sn phase obstruct dislocation glide, leading to dislocation pileups and higher resistance to plastic flow and increased stress amplitude—known as cyclic hardening. The appearance of curved and linear dislocations after fatigue at the elevated temperature indicates thermally activated processes. Non-basal slip improves fatigue resistance by promoting uniform deformation and delaying localized damage.