Low-energy, Mobile Grain Boundaries in Magnesium

Xiangli Liu,Jian Wang

doi:10.1038/srep21393

Abstract

The strong basal texture that is commonly developed during the rolling of magnesium alloy and can even increase during annealing motivates atomic-level study of dislocation structures of both <0001> tilt and twist grain boundaries (GBs) in Magnesium. Both symmetrical tilt and twist GBs over the entire range of rotation angles θ between 0° and 60° are found to have an ordered atomic structure and can be described with grain boundary dislocation models. In particular, 30° tilt and twist GBs are corresponding to energy minima. The 30° tilt GB is characterized with an array of Shockley partial dislocations bp:-bp on every basal plane and the 30° twist GB is characterized with a stacking faulted structure. More interesting, molecular dynamics simulations explored that both 30° tilt and twist GBs are highly mobile associated with collective glide of Shockley partial dislocations. This could be responsible for the formation of the strong basal texture and a significant number of 30° misorientation GBs in Mg alloy during grain growth.

Highlights

The strong basal texture that is commonly developed during the rolling of magnesium alloy and can even increase during annealing motivates atomic-level study of dislocation structures of both tilt and twist grain boundaries (GBs) in Magnesium
We calculated the excess potential energy of < 0001> symmetrical tilt GBs and (0001) symmetrical twist GBs (referred to as (0001)-GBs) in Mg as a function of rotation angle θ, as shown in Fig. 1 (Approaches of assembling gain boundaries are described in Figure S1 in Supplementary)
Between 0° and 60°, there is only one minimum energy GB at the rotation angle 30°. This is consistent with Electron Back Scatter Diffraction (EBSD) observations that a significant number of boundaries with 30° misorientation about the < 0001> direction is characterized in Mg alloy AZ31B during grain growth[11]; and satisfies the energetic criterion: low energy GBs favorably grow during annealing

Summary

Introduction

The strong basal texture that is commonly developed during the rolling of magnesium alloy and can even increase during annealing motivates atomic-level study of dislocation structures of both tilt and twist grain boundaries (GBs) in Magnesium. Molecular dynamics simulations explored that both 30° tilt and twist GBs are highly mobile associated with collective glide of Shockley partial dislocations This could be responsible for the formation of the strong basal texture and a significant number of 30° misorientation GBs in Mg alloy during grain growth. The main objective of this study is to characterize structures and migration mechanisms of both < 0001> symmetrical tilt and twist grain boundaries at atomic level Such studies may provide insightful knowledge into understanding formation and evolution of the basal texture in Mg alloys

Objectives

Methods

Results

Conclusion