The dislocation-twin interaction and evolution of twin boundary in AZ31 Mg alloy

The reaction of lattice dislocation with twin boundary plays a crucial role in the plastic deformation of magnesium alloys. In this study, we visit the basal dislocation-twin interaction in a hot-rolled AZ31 sheet through pre-compression along rolling direction (RD) and subsequent compression along 45° of RD and normal direction (ND), with focus on the twin boundary (TB) structure evolution and nucleation structure characterization. It is found that basal dislocation slip dominates the compression deformation when the strain along 45° of RD and ND is less than 14%; when the strain reaches 14%, new deformation modes are initiated. When the strain is in the range of 5%-14%, basal-prismatic (BP/PB) boundaries are created by dislocation-twin interaction. Meantime, the number of the BP/PB boundaries increase linearly with strain, leading to an extremely incoherent TB. When the strain reaches 14%, {101¯2} twin nucleates from parent of previous {101¯2} twin and {303¯4} twin, a twinning mode not reported before, nucleates from previous {101¯2} TB. Based on the direct experimental observations, the nucleation mechanisms of the new nucleuses are proposed. Moreover, TBs of these new nucleuses present faceted structures and previous {101¯2} twin-new {303¯4} twin interaction results in a low-angle asymmetrical tilt boundary. These correlations will significantly benefit the development of crystal plasticity modeling and enhance meso-scale understanding of structural evolution in hexagonal close-packed materials.

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