Deformation Mechanism of Non-textured and Basal-textured Polycrystalline Mg Alloys: A Coupled Crystal Plasticity-Twinning Phase Field Simulation

Abstract

In this work, an improved crystal plasticity coupled twinning phase field is developed by introducing a hyperbolic hardening function describing the hardening resulting from dislocation slipping interactions. This model effectively captures the complex interactions of multiple plasticity mechanisms in non-textured (NT) and basal-textured (BT) polycrystalline Mg alloys under monotonic and tension-compression cyclic loadings. The results indicate that NT polycrystalline Mg alloy exhibit multi-mode plastic deformation combining basal/non-basal slipping and twinning due to random grain orientations, whereas BT polycrystalline Mg alloys predominantly activate one or two plastic deformation modes including the basal slipping, and the texture angle α (characterized the statistical average properties of the grain orientations) modulates plastic mechanism with selective sensitivity. Cyclic loading reveals tension-compression symmetry in NT and BT (α = 45°) systems, but asymmetry in BT (α = 0°/90°) due to alternating plastic mechanisms. De-twinning-induced nonlinear unloading emerges in both NT and BT polycrystalline systems, and inhomogeneous stress near grain boundaries and twin intersection regions impedes complete de-twinning, accumulating residual twins that facilitate subsequent nucleation. Dislocation slipping, particularly the basal slipping, accommodates strain incompatibility at grain boundaries and around twins, and demonstrates dual roles on twinning. Neighboring grain interactions induce anomalous local deformation inconsistent with the Schmid's law. These findings establish microstructure-property relationships supporting the development of texture-based strengthening-toughening strategies for Mg alloys.