Influence of stress state on microstructure evolution of AZ31 Mg alloy rolled sheet during deformation at room temperature

In this paper, two kinds of micro-tensile test systems for in-situ Electron Back-Scattered Diffraction (EBSD) are developed to explore the difference in microstructure evolution of AZ31 alloy under biaxial tensile stress state (BTSS) and uniaxial tensile stress state (UTSS). The in-situ EBSD results show that there is an apparent difference of texture evolutions during deformation under BTSS and UTSS and the different responses of tensile twins (TTs) in various stress states are proved to be the main reason. A modified calculation of Schmid factor (SF) for varied stress states further reveals that the distribution of TT SF on {0001} pole figure (PF) determined by BTSS significantly differs from that under UTSS. In addition, the change of stress states also affects the deformation compatibility of TT to slip systems. The poor formability of Mg alloy rolled sheets partly results from the incompatibility between TT and slip systems or tensile twinning under BTSS.