Effect of annealing time on bimodal microstructures and tensile properties of Mg–6Sn–3Al–1Zn alloy

Abstract

Although the Mg–6Sn–3Al–1Zn alloy with bimodal grain size distribution has excellent mechanical properties, its mechanical properties can further be improved by adjusting or controlling its microstructures through annealing. In this study, the effect of annealing time on microstructures and mechanical properties of the Mg–6Sn–3Al–1Zn alloy was systematically studied. The Mg–6Sn–3Al–1Zn alloy with bimodal microstructures was prepared through pack-rolling with two passes at 450 °C (55 % thickness reduction per pass, and the total rolling deformation is 80 %). Then the alloy was annealed for 10 min, 20 min, 30 min and 40 min at 350 °C, respectively. The results showed that volume fractions of Mg2Sn phase and recrystallization grains increased with increasing of the annealing time. The multi-modal microstructures were formed in alloys after annealing. When the annealing time ≤30 min, the average grain size of the alloy increased with increasing of the annealing time, while it decreased after annealed for 40 min. The intensity of {0001} texture decreased with increasing of annealing time (<20 min), which caused by dynamic recovery. When the annealing time reached 30 min, the generation of recrystallization led to the enhancement of {0001} texture. However, the {0001} texture intensity reduced after the alloy was annealed for 40 min, which caused by further dynamic recrystallization. In Mg–6Sn–3Al–1Zn alloy annealed for 30 min, the volume fractions of Mg2Sn phase and recrystallization grains were respectively 1.29 % and 56 %, and the average grain size was 6.28 μm. Moreover, the mechanical properties of the alloy reached optimum, i.e., the tensile strength, yield strength and elongation were 336 MPa, 194 MPa and 26 %, respectively.