# The Strain Heterogeneity and Microstructural Shear Bands in AZ31B Magnesium Alloy
###### Abstract  
In this study, the strain distribution and microstructural evolution of the AZ31B magnesium alloy were analyzed via uniaxial tensile loading combined with an in situ tensile test. The results conclusively showed that the strain on the AZ31B magnesium alloy's surface is not uniform during tensile loading in a specific direction, and the emergence of localized twins fosters the development of densely intersecting shear bands, whereas prismatic slip intensified the strain concentration within these bands, ultimately bolstering their strength. These densely packed, discrete shear bands exhibited a dual role: they stabilized plastic deformation processes while simultaneously contributing to material failure. By elucidating the intricate relationship between grain orientation, evolution of the microstructure, and mechanical properties, we could effectively mitigate the detrimental orientations and deformations in anisotropic-polycrystalline materials to enhance their plasticity. The research carries paramount scientific significance and is the key to maximizing the engineering application potential of the AZ31B magnesium alloy. strain heterogeneity; microstructural shear bands; twin; slip system 2020  
and relatively modest strain hardening owing to their high critical shear stress [10; 11]. Conversely, under tension of the lattice C-axis, tension twins of the [10\(\overline{1}\)2] type dominate the initial deformation stage, resulting in a decreased flow stress due to their lower critical resolved shear stress (CRSS). As dislocation-dislocation and dislocation-twin interactions intensify, a marked increase in the strain hardening rate occurs during the later deformation stages, resulting in the characteristic \"S\"-shaped mechanical curve [12; 13]. The complexity and anisotropy of the deformation mechanism result in non-uniform strain distribution in magnesium alloys, which is a critical indicator of material failure. Therefore, it is crucial to have a clear understanding of the non-uniformity of strain and micro-deformation in magnesium alloys under external forces. Currently, most studies analyze the activation of different twin variants in magnesium alloys using electron back scattering diffraction (EBSD) to reveal their deformation mechanisms [14; 15]. [PERSON] et al. studied the [10\(\overline{1}\)1]-[10\(\overline{1}\)2] twin variant and proposed that the observed secondary twins are almost entirely variable with grain boundary orientation differences of 37.5\({}^{\circ}\) or 69.9\({}^{\circ}\), respectively [14]. [PERSON] et al. further pointed out that Schmidt's law and local strain regulation are key factors determining the primary and secondary twin variant selection for deformed magnesium alloys [15]. From a macroscopic standpoint, Digital Image Correlation (DIC) strain mapping has emerged as a valuable tool for the multi-scale investigation of magnesium alloy deformation. Studies employing this technique have consistently revealed a proneness to deformation/shear bands [16; 17]. Notably, recent research has linked these bands to twins, which in turn facilitate <<a>> dislocation slip, thereby enhancing the material plasticity in a beneficial manner [18; 19]. The <<a>> slip refers to the phenomenon of dislocation slipping along the <<a>> direction in a close-packed hexagonal crystal (HCP). In HCP crystals, dislocation slip directions can be categorized into basal (<<a>>), prismatic (<<c>>), and pyramidal (<<a>>) dislocations. Among these, the <<c+a>> dislocation specifically denotes simultaneous slipping along both the c-axis and a-axis directions, thereby providing additional slip systems that enhance the material's plasticity [20]. Understanding the intricate interplay between twins, strain heterogeneity, and material properties represents a crucial step towards optimizing magnesium alloy performance.