Micromechanical behavior and heterogeneous deformation induced hardening of a novel orientationheterostructured Mg-Y alloy

Magnesium alloys usually exhibit poor ductility because of their limited slip systems at room temperature. To overcome this intrinsic limitation, heterostructure design has emerged as an effective strategy for enhancing their mechanical performance, yet the development of orientation-based heterogeneous magnesium alloys remains relatively unexplored. In this work, by varying the triaxial cyclic compression (TCC) applied to an extruded Mg-2.9Y (wt.%) alloy, we obtained two materials that possessed comparable bimodal grain-size characteristics but showed notable differences in orientation heterogeneity. The material processed by TCC along three orthogonal directions for five complete cycles exhibited a predominantly hard orientation, with hard refined grains embedded within coarse grains of the same hard orientation. By applying an additional compression to plane A, the other material mainly comprising the soft orientation was obtained, with hard-oriented refined grains embedded in soft-oriented coarse grains. These materials exhibited quite different tensile properties and work hardening abilities. By combining microstructural characterization and crystal plasticity modeling, deformation micromechanism of the materials under tensile loading was explored. In the former, poor deformation coordination between the different domains led to strain localization in the refined grain region. However, the latter experienced a significant orientation transition due to tensile twinning. This promoted non-basal slip and improved deformation compatibility, resulting in the more persistent hetero-deformation induced hardening. These findings provide fundamental insights into the micromechanical behavior of heterostructured alloys and offer a new strategy for designing high-performance hexagonal close-packed materials by introducing heterogeneous orientation distributions.