Investigation on Cryogenic Tensile Deformation Behavior and Microstructure Evolution in Bimodal Non-Basal Textured AZ31 Mg Alloy Sheet

An AZ31 magnesium (Mg) alloy sheet with a bimodal non-basal texture (BNT sample) exhibits significant potential for a lightweight component design in the aerospace field. However, its mechanical properties and microstructure characteristics during plastic deformation under service conditions when approaching cryogenic temperatures have not been thoroughly investigated. Aiming to elucidate this issue, cryogenic tensile experiments were conducted on a BNT sample and its control group (BT sample), which possesses the typical basal texture. Furthermore, relationships between the underlying deformation mechanisms and the deformation behavior of studied sheets were investigated through a synergistic approach combining a variety of characterization techniques with visco-plastic self-consistent (VPSC) simulations. The BNT sample shows 109.1% higher ductility (~0.23 fracture elongation, FE) but 40.2% lower 0.2% proof yield stress (YS) (~155 MPa) than its BT counterpart during cryogenic tensile deformation. As for the BNT sample, initial deformation is governed by a basal ⟨a⟩ slip and {10-12} extension twin (ET). The latter mainly contributes to accommodate intergranular plastic deformation, and this role cannot be captured in VPSC modeling. Subsequent activation of unusual {10-12}-{10-12} double twin (DT), instead of pyramidal <c+a> slip, enhances strain accommodation, boosting ductility. The discrepancy between simulation and experimental results also primarily stems from the lack of explicit incorporation of {10-12}-{10-12} DT.