Improvement of tension/compression asymmetry for high-performance ZK61 magnesium alloy rod via tailoring deformation parameters: Upsetting-extrusion temperature and upsetting ratio

Abstract

Abstract Upsetting-extrusion (UE) process effectively prepared high-strength ZK61 magnesium alloy rods with tension/compression symmetry. The influence of upsetting-extrusion temperature and upsetting ratio on microstructure was studied. Microstructure evolution in the UE process included two stages: {10–12} tensile twinning significantly divided and refined the coarse grains in upsetting stage, forming a //ED (extrusion direction) texture component; grain refinement suppressed the inverse occurrence of {10–12} tensile twinning during extrusion stage, promoting multi-slip deformation and dynamic recrystallization (DRX) and leading to the diffused {0001}//ED texture. Lowering temperature and increasing upsetting ratio played positive roles in twinning division and DRX refinement. Both of them were beneficial to basal texture weakening which could effectively inhibit the activation of tensile twinning during compression, and promote basal slip contribution during tension, thus improving tension/compression asymmetry. The relationship between microstructure and tension/compression yield strengths was analyzed by texture-dependent Hall-Petch relationship composed of slip and twinning deformation mechanisms. Only slight weakening of the extruded fiber texture was required for tension/compression symmetry for fine-grained structure; but it was the opposite for coarse-grained structure. Correspondingly, only smaller critical upsetting ratio was needed at lower upsetting temperature.