Heterogeneous Deformation-Induced Strengthening Achieves the Synergistic Enhancement of Strength and Ductility in Mg-Sc Alloys

Magnesium alloys are important lightweight structural materials in engineering applications. However, conventional single-phase hexagonal close-packed (HCP) magnesium alloys exhibit poor plastic deformability and insufficient strength at room temperature, which limits their widespread application. In contrast, Mg-Sc alloys with a dual-phase structure (HCP + BCC) demonstrate significantly improved plastic deformability at room temperature compared to single-phase HCP magnesium alloys. In this work, the deformation behavior of dual-phase Mg-19.2 at.% Sc alloy was investigated, revealing its deformation characteristics and multiscale strengthening mechanisms. With increasing heat treatment temperature, the volume fraction of the β phase gradually increased. When the β phase fraction reached 80%, the alloy exhibited the optimal combination of strength and plasticity (ultimate tensile strength: 329 MPa, elongation: 20.5 %). Microstructural analysis reveals that the plastic incompatibility between α/β phases results in significant heterogeneous deformation-induced (HDI) strengthening. The unique bimodal grain size distribution, with the average grain size of the α phase significantly smaller than that of the β phase, further amplified the HDI strengthening contribution by enhancing the "hard phase harder, soft phase softer" heterostructure effect. This study provides new theoretical guidance for designing high-performance dual-phase magnesium alloys from the perspective of multiphase interface engineering.