The Mg–6Sn–3Al–1Zn (wt%) alloy was prepared by casting and then deformed by hot extrusion at 350 °C with different extrusion ratios (9:1, 13:1, 20:1), extrusion rate was 20 mm min⁻¹. The microstructure of as-extruded alloy was analyzed by XRD and EBSD, the tensile properties were tested by a universal testing machine. The results showed that there underwent processing hardening and recrystallization softening simultaneously during the process thermal deformation. Dynamic recrystallization (DRX) mainly occurred at the grain boundary of the deformed grain, with the extrusion ratio increased, the volume fraction of the dynamic recrystallization grain of alloy increased. When the extrusion ratio was less than or equal to 13:1, the average grain size decreased with the extrusion ratio increased. When the extrusion ratio reached up to 20:1, the average grain size increased. {0001} basal plane texture formed after the alloy extruded, and it paralleled to the extrusion direction, the texture intensity decreased first and then increased as the extrusion ratio increased. With the extrusion ratio increased from 9:1 to 20:1, the tensile properties increased first and then declined. Among all the tested alloys, the alloy with the extrusion ratio of 13:1 exhibited the optimum mechanical properties, the yield strength, tensile strength and elongation of alloy was 320 MPa, 371 MPa and 13.5%, the texture strength of the alloy was 8.26, the average grain size was 1.5 μm.

The Mg-6Sn-3Al-1Zn alloys treated with the solid solution were induced 25%, 45%, 65% and 85% rolling deformation at 400 °C, respectively. The microstructures of as-rolled magnesium alloys were analyzed by XRD, OM, SEM and TEM, the mechanical properties were also measured. The results revealed that the rolled Mg-6Sn-3Al-1Zn alloys were composed of α-Mg matrix phase and Mg₂Sn second phase, Mg₂Sn distributed at the grain boundaries and intra-grains. With the increasing of the rolling deformation, the volume fraction of Mg₂Sn phase distributed at the grain boundaries firstly decreased and then stabilized, the average size of Mg₂Sn phase firstly increased and then decreased, the Mg₂Sn phase distributed inside the grains gradually transformed from a rod shape to a spherical shape, the volume fraction of the recrystallized grains gradually increased and the average size of the recrystallized grains early decreased and eventually almost unchanged. When the rolling deformation exceeded 25%, the value of tensile strength and Vickers hardness of the Mg-6Sn-3Al-1Zn alloys increased with the rolling deformation. However, when the rolling deformation exceeded 65%, the elongation of the magnesium alloys diminished, however, the strength of as-rolled magnesium alloys did not increase significantly when the amount of rolling deformation increased from 65% to 85%. The mechanical properties were the best when the amount of rolling deformation reached 65%. Meanwhile, the volume fraction and area of Mg₂Sn phase distributed on the grain boundaries were 2.9%, 105.5 μm², the volume fraction and average grain size of recrystallized grains were 87% and 2.2 μm, respectively. In addition, it was worth noting that the Mg₂Sn phase distributed inside the grains was radically converted into a spherical shape, and the tensile strength, elongation, hardness of the alloy were 317 MPa, 13% and 77.52 HV, respectively.

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.