Role of <a> and <c+a> dislocations on the room-temperature grain boundary migration in a deformed Mg alloy

During deformation, dislocation movements at grain boundaries (GBs) directly affect GB plastic behaviors, thus affecting the mechanical properties of metal materials. As common defects in deformed Mg alloys, the specific role of <a> and <c+a> dislocations on room-temperature GB migration is still unclear. This work systematically investigates and answers this scientific question via experimental observations and atomic simulations. High-density serrated GBs of the AZ80 Mg alloy are achieved by multi-axial compression at room temperature. At the atomic scale, the overall slip of interfacial <a> dislocations leads to GB migration, while the GB can remain flat. Different local migration rates caused by slip and interlock of adjacent <a> and <c+a> dislocations result in GB steps, thus forming the serrated GB as the deformation proceeds. The basal-pyramidal lock at the GB prevents the continuous migration of the local GB. A new basal-pyramidal lock model at the GB is established to give a criterion for stable interlock of partial <a> and <c+a> dislocations. The experimental results and the atomic simulations show good agreement at the atomic scale and atomic simulations can explain the GB structure changes observed in the experiments. This work contributes to understanding the GB migration mechanisms of Mg alloys, which helps design deformed Mg alloys through GB engineering.