Strain hardening due to {10 12} twinning in pure magnesium

Abstract

The effect of grain segmentation by mechanical twinning on the strain-hardening behaviour of textured and random polycrystals is assessed using the Kocks-Mecking method of analysis. Profuse twinning in the first 6–8% strain in textured polycrystals has relatively small strengthening effects despite the large volume fraction of grains undergoing twinning. This is due to the small value of the Hall–Petch constant in textured polycrystals. For random polycrystals, the Hall–Petch constant is much larger but the overall hardening effect is reduced due to the small volume fraction of grains undergoing twinning. Additional hardening effects due to the twinning crystallographic transformation on dislocation mobility are deemed small in cast polycrystals due to their low dislocation density, but may be more important in textured polycrystals with higher dislocation densities. Grain size-independent storage of dislocations accounts for the strain hardening at large strains.