Temperature and solute dependency of conventional {101¯1} twinning shear in Mg

Abstract

The shear deformation accommodated by twins is relevant to the Burgers vector of twinning dislocation (TD). However, according to the climbing image nudged elastic band (NEB) calculation, the edge 4-layer TDs which induce the conventional shear of {10$\overline{\text{1}}$1} twin experience a substantially higher energy barrier to nucleate, by contrast to the mixed 2-layer type. Here, the critical factors (temperature and solute) on 4-layer TD formation have been symmetrically discussed in Mg alloys via molecular dynamics (MD) simulations and theoretical analysis. The thermal driving force is requisite for 4-layer TD nucleation and movement, along with the higher temperature, the lower critical resolved shear stress (CRSS). Moreover, the solute softening or hardening is revealed to be sensitive to the element type, substituted position and concentration. Based on the activation energy barrier and CRSS, the solute softening by 4-layer TD is most obvious when the solutes lie on the second adjacent layer of TB for solute Y, followed by solute Li. The CRSS of TD nucleation decreases obviously with the increased solute proportion in Mg-Y alloy. This work manifests fundamental influencing factors on the {10$\overline{\text{1}}$1} TDs with edge characteristics, which could provide further guidance to operate the conventional shear in Mg and optimize the mechanical features of structural materials.