Experiment and crystal plasticity analysis on plastic deformation of AZ31B Mg alloy sheet under intermediate temperatures: How deformation mechanisms evolve

In order to investigate the evolution of deformation mechanisms of AZ31B Mg alloy sheet and their correlation with material property development under intermediate temperatures, systematic experimental examination and in-depth crystal plasticity analysis on the material are performed. The mechanical responses of AZ31B Mg alloy sheet are measured under uniaxial tension and compression along RD (rolling direction), TD (transverse direction) and ND (normal direction) directions and over the temperature range 100 ∼ 300°C. The evolution of anisotropy (r-value), texture, and microstructure with respect to temperature and strain are examined. Two uncommon deformation behaviors in AZ31 sheet deformation are observed in the experiments for the first time. Firstly, the slope of r-value versus strain curve in RD compression at lower temperature changes from a positive to a negative one when temperature rises to 200°C and 300°C. Secondly, micro-bands are formed during RD compression at 200°C, in contrast to uniform equiaxed dynamic recrystallization (DRX) grains in RD tension and ND compression. The evolution of deformation mechanisms in the uniaxial tension/compression deformation is analyzed with the visco-plastic self-consistent (VPSC) model that takes the variation of r-value into account. The correlation between the experimental observations and deformation modes evolution is probed. It is found that the negative slope of activity ratio of prismatic to basal slip is highly consistent with the change in r-value with strain during uniaxial compression at 200°C. The different rotation ‘room’ caused by basal slip in uniaxial compression at 200°C, together with the restriction of grain boundary, leads to higher misorientation evolution rate in loading direction than in the other directions, and then results in the formation of micro-bands.