Asymmetry evolutions in microstructure and strain hardening behavior between tension and compression for AZ31 magnesium alloy

This work investigated the asymmetry evolutions in the microstructure and the plastic deformation behavior between the entire tension and compression for AZ31 magnesium alloy by combining the experiment and visco-plastic self-consistent (VPSC) model. Large yield stress asymmetry between the tension and the compression existed at the onset of plastic deformation, but such stress asymmetry slightly increased first and then gradually decreased to 1.01 with the increase of logarithmic plastic strain. This kind of asymmetry variation was ascribed to the microstructure evolution asymmetry. Compared to the tension deformation, tension twin boundaries migrated more easily in the compression deformation owing to the appropriate crystal orientation, producing more obvious fraction variation of tension twin boundary and the intersection of different tension twin variants. The VPSC model clarified the texture evolution asymmetry between the tension and the compression by the contribution of each deformation mechanism to the macroscopic strain, revealing that prismatic slip activation in the tension triggered the development of ⟨101‾0⟩//LD (LD: loading direction) type texture while abundant tension twinning in the compression laid the foundation of ⟨0002⟩//LD type texture. Additionally, owing to the deformation mechanism transformation from basal slip to prismatic slip in tension deformation, the attenuation degree in the strain hardening rate was gradually weakened, while in compression deformation, the participation of elastic deformation contributed to the increasing stage of strain hardening rate after the exhaustion of tension twinning. In addition, the geometrical orientation factor and deformation mechanism factor together contributed to the decline of flow stress asymmetry.