Fig 1. Microstructure of as-extruded ZM21 magnesium alloy (a) optical microstructure, (b) grain size distribution in (a), (c) local IPF map in ED-ND section (d) (0001) pole figure.

Fig 2. (a) Schematic location of the tensile samples in extruded sheet, (b) dimensions of the in-situ tensile specimens (unit: mm), (c) stress-displacement curve of the specimen.

Fig 3. Macro-morphology of the edge cracks of ZM21 alloy sheets after rolled with different pass reductions (a) 30%, (b) 45%, (c, e) 60%, and the cracks only on the RD-ND plane are shown by red arrows in (e), (d, f) 75% and the cracks only on RD-ND plane are shown by red arrows in (f).

Fig 4. Surface appearance on ND-RD section of the rolled specimens with reductions of (a) 30% and the surface groove is illustrated by the arrow, (b) 45% and the minor crack is presented by the arrow, (c) 60%, (d) 75%.

Fig 5. Microstructures of RD-ND sections for ZM21 alloy sheets after rolled with different reductions of (a) 30%, (b) 45%, (c) 60%, (d) 75%; (e), (f), (g), and (h) are corresponding grain diameter distribution, respectively.

Fig 6. Micro edge cracks in the ND-RD plane at a single pass reduction of 60% (a), (d) Inverse pole figure (IPF) map; (b), (e) corresponding recrystallization map in (a), (d), respectively; (c), (f) corresponding Kernel average misorientation (KAM) map in (a), (d), respectively.

Fig 7. Macro SEM morphological evolution of the ZM21 alloy during the in-situ tensile experiments at 150 °C (a) 0.37 mm, (b) 0.46 mm, (c) 0.56 mm, (d) 0.75 mm and some visible micro-holes are presented by arrows, (e) 0.79 mm, (f) final fracture. The tensile loading direction is horizontal.

Fig 8. SEM images of ZM21 alloy tensile deformed at 150 °C with different displacements, (a) 0.37 mm, (b) 0.46 mm, (c) 0.56 mm and some micro-cracks are shown in the white arrows, (d) 0.75 mm, (e) 0.79 mm; and the large grains are marked with red arrows in (d) and (e); (f) the magnified view of the marked region in (e); and the twins are marked with green arrows.

Fig 9. In-situ scanning images at various displacements (a) 0.37 mm, (b) 0.46 mm, (c) 0.56 mm, (d) 0.75 mm; and cracks are also marked with red arrows in (c), (d); and (e), (f), (g), and (h) are their corresponding inverse pole figures (IPF) map, respectively.

Fig 10. Recrystallization maps at various displacement levels (a) 0.37 mm, (b) 0.46 mm, (c) 0.56 mm and (d) 0.75 mm; (e), (f), (g) and (h) are their corresponding Kernel average misorientation maps, and high stress concentration areas are labeled by dotted ellipses in (g); (i), (j), (k) and (l) are their corresponding distribution of KAM value.

Fig 11. In-situ SEM images and inverse pole figures (IPF) of ZM21 in-situ tensile sample at 150 °C with different displacements, (a) 0.37 mm, (b) 0.46 mm, (c) 0.56 mm, (d) 0.75 mm, and the crack area is marked with the dotted ellipse; (e), (f), (g) and (h) are their corresponding inverse pole figure (IPF) maps.

Fig 12. In-situ SEM maps of the local magnified area around cracks in Fig. 11 at various displacement levels (a) 0.37 mm, (b) 0.46 mm, (c) 0.56 mm and the obvious slip trace is marked by the yellow arrow, the grain distortion and surface buckling are marked with white arrows; (d) 0.75 mm, a twin in G13 and some cracks are labeled, as shown in yellow arrows; (e), (f), (g) and (h) are their corresponding IPF maps and pole figures; (i), (j), (k) and (l) are their corresponding recrystallization maps; (m), (n), (o) and (p) are their corresponding Kernel average misorientation (KAM) maps.

Fig 13. Schematic diagram of the stress state for the sheet during deformation, (a) the rolling and the stress state at the center and edge of the sheet during the rolling (b) the stress state of in-situ tensile test.

Fig 14. (a) Local IPF maps at the displacement of 0.37 mm, (b) twins situation in (a), and (c) the Schmid factor for basal slip in the selected area, (d) grain orientation around the cracks.

Fig 15. Partial grains at the displacement of 0.37 mm (a) IPF map, and (b) the Schmid factor for basal slip, (c) grains orientation around the triple junction of grain boundaries with the dotted line in (b).