Abstract
Effects of extrusion temperature on microstructure and mechanical properties of low Zn and rare earth (RE) containing Mg-2.5Zn-0.7Y-0.4Zr alloy were investigated. It was subjected to indirect extrusion at 300°C and 350°C at low extrusion speed (0.3mm/s). The microstructures of as-extruded alloys exhibited both a bimodal grain structure consisting of refined dynamic recrystallized (DRXed) grains and elongated strips of non-recrystallized (un-DRXed) grains. Additionally, the fragmented Mg3Zn2Y3 (W) phase particles distributed along the extrusion direction and promoted dynamic recrystallization. Meanwhile, the amount of nanoscale MgZn2 and W phases were dynamically precipitated in Mg matrix during the extrusion process. The average size and volume fraction of DRXed grains decreased with the extrusion temperature decreasing from 350°C to 300°C, while the volume fraction of precipitates increased. The alloy extruded at 300°C exhibited superior mechanical properties with the ultimate tensile strength (UTS) of 347.1MPa, yield strength (YS) of 329.3MPa and elongation (EL) of 12.8%. The enhancement of yield strength was mainly attributed to fine DRXed grains and dense nanoscale precipitates. The strengthening mechanism and microstructure evolution were also discussed.
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