Enhanced mechanical properties of Mg-Zn-Y-Zr alloy by low-speed indirect extrusion

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 degrees C and 350 degrees C at low extrusion speed (0.3 mm/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 degrees C to 300 degrees C, while the volume fraction of precipitates increased. The alloy extruded at 300 degrees C exhibited superior mechanical properties with the ultimate tensile strength (UTS) of 347.1 MPa, yield strength (YS) of 329.3 MPa 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. (C) 2020 The Author(s). Published by Elsevier B.V.