Tension-compression asymmetry of extruded Mg-Gd-Y-Zr alloy with a bimodal microstructure studied by in-situ synchrotron diffraction

In this work, the tension-compression asymmetry of an extruded Mg-8.4wt.%Gd-2.3wt.%Y-0.2wt.%Zr alloy with a bimodal microstructure, consisting of fine DRXed grains and coarse unDRXed grains, was investigated by in-situ synchrotron diffraction testing and microstructure analysis. It is found that the as-extruded alloy exhibits good tension-compression yielding symmetry, which is attributed to the same deformation mechanisms (prismatic and basal slip) governing the tensile and compressive yielding. However, the strain hardening response after the macroscopic yielding is different under tension and compression, since tensile twinning, which mainly occurs in the unDRXed grains, makes an important contribution to the deformation under compression, but not under tension. The alloy shows a somewhat linear strain hardening after yielding under compression, which is mainly due to the inhibition of tensile twinning and enhancement of prismatic slip. The suppression of tensile twinning mainly results from the high concentration of rare earth solute elements, weak texture and grain refinement of the DRXed regions. This work suggests that the tension-compression asymmetry of Mg alloys can be effectively reduced by the addition of rare earth elements and grain refinement. (C) 2019 The Authors. Published by Elsevier Ltd.