Shengwen Bai

The {10-12} tensile twinning dominates the strength and plasticity of magnesium (Mg) alloys, yet the effect of grain boundary (GB) character distribution remains underexplored. This work combines quasi-in situ EBSD and molecular dynamics (MD) simulations to investigate how misorientation affects twinning transmission and mechanical properties in AZ31B alloy. The results revealed that Low-angle GBs (10°<θ<30°) facilitate twin pair or twin band formation, weakening resistance to twin propagation and lowering strength. In contrast, interactions between twin boundaries and high-angle GBs (θ<30°) induce heterogeneous strain buildup, raising back stress and critical stress for twin motion, thus strengthening the alloy. Samples rich in low-angle GBs exhibit deformation deviating from the Schmid factor (SF) criterion, due to weak GB hindrance and enhanced non-SF twinning. Furthermore, the selection of twinning variants in the twinning bands was jointly governed by the geometric compatibility factor (m') and Schmid factor (SF). This research provided a foundational understanding for further exploration of the relationship between twinning behavior and the mechanical properties of Mg alloys.

The {10-12} tensile twinning dominates the strength and plasticity of magnesium (Mg) alloys, yet the effect of grain boundary (GB) character distribution remains underexplored. This work combines quasi-in situ EBSD and molecular dynamics (MD) simulations to investigate how misorientation affects twinning transmission and mechanical properties in AZ31B alloy. The results revealed that Low-angle GBs (10°<θ<30°) facilitate twin pair or twin band formation, weakening resistance to twin propagation and lowering strength. In contrast, interactions between twin boundaries and high-angle GBs (θ<30°) induce heterogeneous strain buildup, raising back stress and critical stress for twin motion, thus strengthening the alloy. Samples rich in low-angle GBs exhibit deformation deviating from the Schmid factor (SF) criterion, due to weak GB hindrance and enhanced non-SF twinning. Furthermore, the selection of twinning variants in the twinning bands was jointly governed by the geometric compatibility factor (m') and Schmid factor (SF). This research provided a foundational understanding for further exploration of the relationship between twinning behavior and the mechanical properties of Mg alloys.

Magnesium alloys are promising candidates for lightweight applications due to their low density and high specific strength, but their room-temperature formability is limited by low ductility, a consequence of the hexagonal close-packed (HCP) crystal structure. Traditional approaches to improve ductility through basal texture weakening often lead to a significant strength reduction, highlighting a persistent strength-ductility trade-off. Furthermore, whether such ductility enhancement stems solely from a favorable orientation for basal slip remains debated. Recent advances suggest that constructing heterostructures may enable synergistic improvement of strength and ductility. In this study, a crystallographic orientation heterostructure was fabricated in an AZ31 magnesium alloy via a compression-annealing process coupled with tailored tensile loading directions, achieving a high elongation of ~32%. An innovative "mechanical-reassembly-testing" methodology is introduced to decouple the individual contributions of crystallographic orientation changes and the heterostructure effect. Results demonstrate that the crystallographic orientation heterostructure plays a dominant role in enhancing ductility. The underlying mechanisms of the ductility improvement were elucidated through quasi-in-situ slip trace analysis, high-resolution digital image correlation (DIC) and full-field crystal plasticity simulations. It is revealed that deformation incompatibility between grains of differing orientations promotes the activation of non-basal slip systems, thereby improving ductility. This work demonstrates that constructing crystallographic orientation heterostructures can significantly enhance ductility without compromising strength, offering a novel pathway to overcome the strength-ductility trade-off in magnesium alloys. These findings advance the fundamental understanding of plastic deformation in HCP metals and provide a theoretical basis for designing high-performance magnesium alloys.