Effect of Temperature on Deformation Mechanisms of AZ31 Mg-alloy under Tensile Loading

Controlled in situ SEM tensile tests have been carried out between 200 and 300 °C at a constant strain rate of 5.10-5 s-1 to investigate the effect of temperature on deformation mechanisms operating in an Mg–3Al–1Zn (AZ31) Mg-alloy. Fiducial microgrids deposited using electron beam lithography are used to evidence grain boundary sliding as well as to determine the spatial strain heterogeneities as a function of temperature. Dislocation creep and grain boundary sliding coexist between 200 and 300 °C but their respective activity varies significantly as shown by the strain rate sensitivity value m which is about 0.2 at 200 °C but about 0.5 at both 250 and 300 °C. In addition, grain boundary sliding becomes predominant at 250 and 300 °C whereas its occurrence is relatively limited at 200 °C. Slip trace analysis shows that at 200 °C prism and pyramidal slip already exhibit a great activity. Spatial strain heterogeneities determined by digital image correlation (DIC) based on microgrid displacements develop during the early stage of plastic deformation and persist at larger strains. It is shown that the strain in the vicinity of grain boundaries intensifies when the temperature rises from 200 to 300 °C while the core of grains accommodates less deformation in agreement with the fact that grain boundary sliding is predominant at 250 and 300 °C.