The mechanisms of grain growth of Mg alloys: A review

Grain growth directly influences the plasticity and strength of Mg alloys. As the grain size decreases from the microscale to the nanoscale, the plasticity of Mg alloys continually increases, whereas the strength first increases and later decreases. These trends are observed because the plastic deformation mechanism changes from dislocation–twinning dominance to grain boundary dominance. In this study, the factors influencing grain growth, such as the temperature of plastic deformation/annealing, second-phase particles and solute atoms, are examined to aid effective control of the grain size. Additionally, the mechanisms of grain growth, typically induced by strain and thermal activation, are clarified. Strain-induced grain boundary migration is attributable to the difference in the strain energy stored in adjacent grains with high-density dislocations. Heat-induced grain boundary migration is driven by the difference in the energy of the grain boundary/subgrain boundary and boundary curvature. Abnormal grain growth can be induced by anisotropy of the strain energy, anisotropy of the grain boundary mobility, depinning of the second phase and high misorientation gradient.