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

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 (0.3 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 °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 347.1 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.

Keywords

• Magnesium alloys
• Microstructure
• Mechanical properties
• Extrusion
• Precipitates