Fig. 1. (a) Inverse pole figure showing the initial microstructure of rolled AZ31 plate and (b) stress-strain curve under tension along rolling direction of AZ31 rolled plate. The dimension of the tension sample is inserted. The samples subjected to EBSD examination were cut from the region indicated by the red rectangular box.

Fig. 2. Typical EBSD results of tensioned samples in band contrast (a) and in verse pole figure map (b); Boundaries of {10$\bar{1}$2}, {10$\bar{1}$1} and {10$\bar{1}$1}-{10$\bar{1}$2} twins are colored in red, dark blue and light blue. (c) Line profiles for the misorientation angle along the direction indicated by the white arrow in Fig. 2(b).

Fig. 3. TEM image showing the feature of deformation twins near fracture region of magnesium alloy. The electron beam is nearly parallel to [11$\bar{2}$0] zone axis. The twins are denoted by Ti (i = 1, 2, 3, 4, 5) and the matrix is marked by M. The selected area diffraction patterns taken from the regions 1, 2, 3, 4 and 5 are presented in Fig. 2 (b-f), respectively. Basal stacking faults within the twins are indicated by the black arrows. The outlines of these deformation twins are denoted by the white lines.

Fig. 4. (a) HRTEM image showing the morphology of a {10$\bar{1}$1} twin tip in deformed magnesium. (b) The corresponding bright-field TEM image at a relatively low magnification is inserted. The selected area electron diffraction patterns focusing on the twinning boundary highlighted by the red rectangular box are also inserted. The electron beam is nearly along [11$\bar{2}$0] zone axis. The (0002) basal and {10$\bar{1}$1} pyramidal planes of T6and M are marked by the black lines. Three types of facets are presented in Fig. 4(a), including {10$\bar{1}$1} coherent twinning boundaries (TBs) marked by the yellow lines, (0002)T|| (10$\bar{11}$) M basal-pyramidal (BPy) and (10$\bar{11}$) T||(0002)M pyramidal-basal (PyB) planes highlighted by the red lines.

Fig. 5. (a) Bright-field TEM image showing the interaction of two {10$\bar{1}$1} twin variants (T6 and T7). The electron beam is nearly parallel to the [11$\bar{2}$0] zone axis. (b) A higher magnification showing the twin-twin interaction presented in Fig. 5(a). The (0002) basal planes of twins and matrix are marked by the yellow lines. Twin-twin boundary (TTB) is indicated by the black arrowhead.

Fig. 6. HRTEM image showing the interaction between two {10$\bar{1}$1} twin variants. The electron beam is nearly parallel to [11$\bar{2}$0] zone axis. The fast Fourier transformation patterns taken from the boundaries of T9 and T10 are inserted at the upper left and lower left corners, respectively. The (0002) basal and {10$\bar{1}$1} pyramidal planes of the twins and matrix are marked by the black lines. The outlines of T9 and T10 are described by different colors. As can be shown, the boundaries of both T9 and T10 consist of {10$\bar{1}$1} coherent TBs, BPy and PyB interfaces. The twin-twin boundary (TTB) formed by the interaction is denoted by the green line.

Fig. 7. Schematic exhibitting the deviation phenomenon caused by the terrace-step structure of {10$\bar{1}$1} twinning boundary (TB). The {10$\bar{1}$1} coherent TBs and BPy interfaces are colored in yellow and red, respectively. The deviation angle is referred to as β.

Fig. 8. Schematic exhibitting the interaction between different two {10$\bar{1}$1} twin variants. Boundaries of T9 and T10 are colored by orange and light blue, respectively. The twinning dislocations (TDs) are presented by the green symbols of “⊥”. The growth of T9 will be impeded as the twin variants approach each other. The twin-twin boundary (TTB) formed is marked by the red line, and the interfacial defects located on it are denoted by the brown symbols of “⊥” .

Fig. 9. Schematic showing the interaction between two {10$\bar{1}$1} twin variants, i.e. T11 and T12. Here, the width of T11 is assumed to be much larger than that of T12. When the tip of T11 approaches the boundary of T12, the growth of a part of T11 will be hindered, while, the tip of the rest part of T11 colored in green in Fig. 9(a) may also continue propagating forward. When this section of movable twin tip bypasses T12, it spreads laterally again, and grows around T12, as shown in Fig. 9(b).