Microstructure and deformation behavior of medium strength and high ductile VW93A Mg alloy profile prepared by high-efficiency extrusion at a higher process temperature

Abstract

Deformation at lower temperatures is the mainstream method for preparing high-strength Mg-Gd-Y-Zn-Zr alloys, but it compromises both deformation conditions and process efficiency. This study reports the preparation of a U-shaped VW93A (Mg-8.8Gd-2.8Y-1.8Zn-0.5Zr) Mg profile, achieving a balance of strength and ductility through high-efficiency extrusion at a safe process temperature (480 °C), followed by rapid cooling (a step to suppress dynamic precipitation). The profile exhibited a tensile yield strength (TYS) of 287 MPa with an exceptional elongation (EL) of 18.5% after extrusion. Upon aging, the TYS further increased to 387 MPa, with a sacrifice in EL to 11.2%. The extruded profile featured a typical heterogeneous microstructure, composed of basal oriented deformed grains (~20%) enriched with needle-like γ'/long period stacking ordered (LPSO) phases, and diverse oriented dynamically recrystallized (DRXed) grains interspersed with sparse lamellar LPSO phases. Quasi in-situ EBSD analysis further revealed that excellent plasticity of alloy was primarily borne by diverse oriented DRXed grains, governed by early-stage basal <a> slip and sustained <c+a> slip and multiple slip proliferation. Besides, the differential deformation between coarse and fine grains promoted the formation of heterogeneous interfaces with higher geometrically necessary dislocation (GND) density, imparting additional hetero-deformation induced (HDI) hardening for the alloy. Unlike the strong heterogeneous interfaces between dissimilar materials, however, the soft heterogeneous interface between coarse and fine grains could also significantly coordinate deformation through strong multiple slip within coarse grains at high strain level, restricting cracks initialization at the interface. Finally, the study found that significant activation of non-prismatic slip and the phase stimulating nucleation (PSN)/pinning effect of bulk/strip LPSO phases under extrusion jointly promoted the formation of an abnormal (0001) texture. During tensile loading, grains with (0001) texture exhibited relatively slow {$10\bar{1}$$10\bar{1}$2} twinning propagation and synergistic multipleslip activation, enhancing the sustained strain hardening during the over yield stage.