Deformation Mechanism of Non-Textured and Basal-Textured Polycrystalline Mg Alloys: A Phase Field Simulation

A crystal plasticity-phase field model is used to investigate the deformation mechanism of non-textured (NT) and basal-textured (BT) polycrystalline Mg alloys under monotonic and tension-compression cyclic loadings. The results indicate that both the basal/non-basal slipping and extension twinning are involved in the plastic deformation of NT polycrystalline Mg alloy, due to the random crystalline orientation of its grains. In contrast, BT polycrystalline Mg alloys, with similar crystalline orientation of all grains, exhibit one or two dominant plastic deformation mechanisms, including the basal slipping. Variations in the texture angle α further influence the plastic deformation mechanism with varying sensitivity to α within different α ranges. Under the tension-compression cyclic loading, the NT and BT (α = 45°) polycrystalline Mg alloys exhibit a tension-compression symmetry; however, the BT polycrystalline Mg alloys at α = 0° and 90° display a tension-compression asymmetry resulting from alternating plastic deformation mechanisms throughout the cyclic loading. The occurrence of de-twinning leads to obvious nonlinear behavior during the unloading in both NT and BT polycrystalline Mg alloys. Twin formation induces significant stress redistribution, impeding the de-twinning due to inhomogeneous stress fields near grain boundaries and twin-twin interaction regions. This leads to an accumulation of incompletely de-twinned twins during cyclic deformation and further provides favorable conditions for twin nucleation. Dislocation slipping, particularly the basal slipping, relieves the local stress, suppressing twinning, while accumulating at grain boundaries to promote twin nucleation. It is also crucial for accommodating the deformation incompatibility between neighboring grains and around twins. Finally, the synergistic deformation between neighboring grains significantly influences the intragranular deformation, potentially leading to an anomalous local deformation inconsistent with the Schmid's law. This study elucidates the texture-related deformation mechanisms of polycrystalline Mg alloys, providing a theoretical foundation for the strengthening and toughening design of Mg alloys.