The effect of strain rate on the mechanisms of plastic flow and failure of an ECAE AZ31B magnesium alloy

Plastic flow is studied as a function of strain rate for uniaxial compression along the principal directions of an AZ31B magnesium alloy processed by equal channel angular extrusion across 8 decades of strain rate. The effect of strain rate on flow stress is found to be a function of loading orientation. Work hardening rates are also found to vary with strain rate and orientation. In situ high-speed imaging reveals the prominence of heterogeneous deformation at small macroscopic strains. Postmortem electron microscopy further shows significant texture reorientation under multiple orientations of loading-some aided by twins and others by dislocation slip. It is observed that twin activity is more favorable at high strain rates. While very little twinning and significant grain growth were observed from complementary quasi-static experiments by Krywopusk et al. (unpublished), we observe significant twinning with negligible grain growth at high strain rates.