Effects of Ca and Sr additions on microstructure, mechanical properties, and ignition temperature of hot-rolled Mg–Zn alloy

In this study, the microstructures, mechanical properties, and ignition temperatures of hot-rolled Mg-1.5Zn-X (X: Ca and/or Sr) alloys were investigated. The Mg-1.5Zn, Mg-1.5Zn–1Ca and Mg-1.5Zn–1Sr alloys had the mean grain sizes of 56.1 μm, 8.7 μm, and 18.5 μm, respectively. This indicates that Ca addition exerts a stronger effect on grain refinement than Sr addition. Both Ca and Sr additions significantly weakened the basal texture to approximately one-quarter in intensity for the annealed sheets. Ca-containing alloys exhibited texture splitting in the transverse direction, while Sr-containing alloys tended to maintain it in the rolling direction after annealing. The Ca and Sr additions improved the mechanical strength considerably due to grain refinement, which overcompensated for the influence of texture softening. Meanwhile, benefiting from the weakened textures, the 1% Ca and Sr additions remarkably increased the Erichsen values from 3.8 to 8.0 and 7.1, respectively. However, further addition resulted in the deterioration of both tensile ductility and stretch formability due to the cracking of secondary-phase particles. Ca addition had a better effect on enhancing the flame-retardant property than Sr addition, and 2% Ca and Sr additions increased the ignition temperature from 629 °C to 800 °C and 720 °C, respectively.