Habit planes of twins in a deformed Mg alloy determined from three-dimensional microstructure analysis

Abstract Serial sectioning and electron backscatter diffraction were used to image the three-dimensional microstructures of Mg alloy AZ31B deformed in tension and compression along sample directions that promote twinning. These measurements were used to statistically determine the habit planes of twin boundaries within the samples. For the sample deformed in tension, the boundary population is dominated by the so-called extension twin (lattice disorientation of 86° about 2 1 ¯ 1 ¯ 0 with symmetric 01 1 ¯ 2 boundary planes) and boundaries formed by the intersection of these defects (lattice disorientation of 60° about 01 1 ¯ 0 with 11 2 ¯ 1 and 01 1 ¯ 1 boundary planes). The sample deformed in compression, however, was different. Fewer twin variants were activated and this led to many fewer intersections and intervariant boundaries. Furthermore, while the dominant boundary also had the lattice disorientation of 86° about 2 1 ¯ 1 ¯ 0 , consistent with an extension twin, the dominant habit planes have the asymmetric 0 1 ¯ 11 and 01 1 ¯ 3 orientations. The difference in the habit planes was attributed to the presence or absence of twin intersections. When many twins intersect, the twins form plate-shaped grains, bounded by two parallel 01 1 ¯ 2 interfaces. Without these intersections, the twins are wedge-shaped, with the bounding 0 1 ¯ 11 and 01 1 ¯ 3 interfaces meeting at a sharp edge.