# The Strain Heterogeneity and Microstructural Shear Bands in AZ31B Magnesium Alloy
## 4 Discussion  
The rolled AZ31 magnesium alloy plate itself has a substrate texture, and when stretched along the C-axis of the grain (the grain is mainly parallel to the ND and TD directions), the C-axis is compressed. This compression satisfies the preconditions of atomic configuration for the formation of compressive twins and is conducive to the formation of high-density compressive twins along the shear direction. At the same time, the formation of twins also requires the flow stress of the material to reach its critical stress. In the uniaxial tensile process, the yield stress of the material is higher than 135 MPa, and the shear stress reaches the peak value when the tensile direction is 45\({}^{\circ}\), and the critical stress of activating the compression twin is easily reached. Therefore, compressive twins are activated when stretched along the C-axis of the grain. The appearance of these compressive twins excites the shear deformation, resulting in a large amount of strain accumulation in the shear direction, forming a shear band. At the same time, due to the diffusion of the slip channel caused by local twins, the dislocation density in the shear band increases, which promotes the generation of additional dislocations. Therefore, the interaction between twins and local grain dislocations eventually leads to the formation of microscopic shear bands, resulting in strain heterogeneity on the specimen surface.  
To scrutinize the nature of slip phenomena, attention was focused on calculating the Schmidt factors for both the basal and prismatic slip systems in the initial sample, with the results presented in Figure 9. The figure reveals that the majority of the grains in the pristine sample exhibited a high Schmidt factor favoring basal plane slip, indicating a prevalent occurrence of basal plane slip across these grains. Conversely, the distribution of Schmidt factors for prismatic slip showed obvious directivity, which aligned well with the orientation and extent of shear bands. In the initial to intermediate stages of tensile deformation, the AZ31B magnesium alloy primarily underwent basal plane slip in most grains. However, grains oriented along the shear direction exhibited a dual-mode deformation characterized by both twinning and prismatic slip. Notably, the dislocation density within the shear zone grains was elevated, indicative of the pronounced deformation in these  
Figure 8: KAM map of a representative area under different strains. (**a**) At 0.01 strain; (**b**) At 0.02 strain; (**c**) At 0.05 strain; (**d**) At 0.12 strain.  
regions. As the deformation progresses to later stages, the dislocation density within the majority of the grains surged, while the defect density in the shear zone grains gradually reached saturation, ultimately leading to material failure.  
Compared with other metal materials, the asymmetric crystal structure of magnesium leads to the formation of texture in the forming process of its alloy materials, and the strain will be heterogeneous in the tensile loading in a specific direction. The combined effect of loading direction and texture leads to strain localization of the AZ31B magnesium alloy. The strain distribution in different loading directions can be studied later to provide guidance for engineering applications. Twin and dislocation can also be introduced through pre-deformation treatment to make the plastic deformation more uniform, avoid strain localization, and improve the plasticity of the material.