Influence of Extrusion Ratio on Microstructure and Tensile Properties of Mg–Gd–Y–Zn–Zr Alloy

In the present work, an Mg–5Gd–4Y–0.5Zn–0.5Zr alloy was extruded at 450 °C with three extrusion ratios of 25, 79 and 178. The microstructure of the as-cast and as-extruded specimens were analyzed by using Optical Microscopy, Scanning Electron Microscopy, Electron Back Scattering Diffraction and X-ray Diffraction, and the mechanical properties were evaluated by uniaxial tensile testing. The as-cast alloy had an average grain size of 26.0 μm. After extrusion, the grain size decreased to less than 5 μm, but it did not decrease monotonically with the increasing extrusion ratio. In the as-cast specimen, secondary phases, including Mg 24 (RE) 5 and α-Zr, distributing along the grain boundaries as well as in the grains, which were broken into finer particles distributed in stripes along the longitudinal direction after extrusion. Moreover, a few Mg 3 RE particles were found in the as-extruded specimens. With the increase of extrusion ratio, the basal texture was weakened successively, and thus the Schmid factor of (0001) slip system increased. As revealed by tensile tests and fracture surface observation, the best comprehensive mechanical properties were acquired with the extrusion ratio of 178, which were 346 MPa, 284 MPa and 40.5% for UTS, TYS and EL, respectively. Having correlated the TYS with grain size, the constants in Hall–Petch formula were determined to be 59.5 MPa for σ 0 and 360.8 MPa μm 1/2 for k . Graphical Abstract