Phase transformation, texture evolution, and mechanical properties of Mg-9.5Gd-4Y-2Zn-0.3Zr alloy wires fabricated using hot drawing

Abstract

Mg-9.5Gd-4Y-2Zn-0.3Zr alloy wires with a diameter of 1.2 mm were fabricated by a multistage drawing process with a cumulative area reduction (CAR) of 96% at 500 °C using as-extruded rods with a diameter of 6 mm as the raw material. Investigated the impact of microstructural transformations on the mechanical performance of these wires, with a focus on phase evolution, texture changes, and grain refinement. In the alloy, second-phase 18R-LPSO, rare-earth-rich (RE-rich) phase, and Zn2Zr3 distributed at the grain boundaries along the extrusion direction (ED) or the drawing direction (DD), which were different from the intragranular 14H-LPSO phase, were observed. Significantly, we observed the transformation of blocky 18R-LPSO phases into sub-2μm W-Mg3Zn3RE2 particles during hot drawing. All the as-extruded and as-drawn wires exhibited equiaxed grains with average sizes between 4 μm and 7 μm. The as-extruded wires exhibited a texture with {0001} perpendicular to ED. As the CAR increased, the texture of the wires transformed into a basal texture with {0001} parallel to DD. The ultimate tensile strength (UTS) and tensile yield strength (TYS), respectively, increased from 369 MPa to 283 MPa for the as-extruded wire to 466 MPa and 436 MPa for the as-drawn wire with CAR increasing to 55%, and then decreased to 328 MPa and 318 MPa for the wire with CAR increasing to 96%. The elongation (EL) reduced from 8.01% to 1.37% with CAR increasing to 96%. As CAR exceeded 55%, the increased volume fraction of the W-Mg3Zn3RE2 phase resulted in a significant decrease in both the strength and the plasticity of the wires. The evolution of microstructure and mechanical properties provides possibility for regulating both the strength and elongation of the Mg-Gd-Y-Zn-Zr alloy wires by optimizing the drawing process.