Synergy of Strength and Plasticity in Extruded VZ91K Magnesium Alloy Achieved by Constructing Bimodal Grain Structure via Suppression of PSN‐DRX

ABSTRACT

Bimodal grain structure (BGS) demonstrates significant potential in synergistically optimizing the strength and plasticity of magnesium alloys. Acquiring the desired BGS consequently became a critical challenge. This study took the Mg‐9Gd‐1Zn‐0.5Zr (wt%, VZ91K) alloy as its subject. From the perspective of BGS formation mechanisms, it suggests an effective strategy for constructing BGS, revealing the associated microstructural evolution, as well as the strengthening and toughening mechanisms. Research indicates that fully dissolving the micron‐sized blocky eutectic phase in the as‐cast alloy can significantly suppress the particle‐stimulated nucleation‐induced dynamic recrystallization (PSN‐DRX) that occurs during extrusion, thereby yielding a BGS in the VZ91K alloy. The VZ91K alloy with BGS exhibits a significant enhancement in yield strength compared to homogeneous alloys (194–268 MPa), accompanied by an acceptable decrease in elongation to fracture (24.5%–20.3%). Hetero‐deformation‐induced (HDI) hardening is the critical factor driving the synergistic strength‐plasticity of the VZ91K alloy with BGS. During tensile deformation, the HDI stress and HDI hardening rate of the VZ91K alloy with BGS consistently exceed those of the homogeneous alloy. Additionally, dislocation strengthening, low‐angle grain boundary strengthening, LPSO, and γ′ phase strengthening are also responsible for the high strength of the VZ91K alloy with BGS. This study presents a novel approach to constructing BGS, which could facilitate its application in the regulation of the mechanical properties of magnesium alloys.