Rejuvenation of plasticity via deformation graining in magnesium

Magnesium, the lightest structural metal, usually exhibits limited ambient plasticity when compressed along its crystallographic c-axis (the hard orientation of magnesium). Here we report large plasticity in c-axis compression of submicron magnesium single crystal achieved by a dual-stage deformation. We show that when the plastic flow gradually strain-hardens the magnesium crystal to gigapascal level, at which point dislocation mediated plasticity is nearly exhausted, the sample instantly pancakes without fracture, accompanying a conversion of the initial single crystal into multiple grains that roughly share a common rotation axis. Atomic-scale characterization, crystallographic analyses and molecular dynamics simulations indicate that the new grains can form via transformation of pyramidal to basal planes. We categorize this grain formation as deformation graining. The formation of new grains rejuvenates massive dislocation slip and deformation twinning to enable large plastic strains. Understanding deformation of Mg along the c-axis is important for wrought processing of Mg. Here the authors report deformation graining in submicron single crystal Mg where the initial single crystal evolves into ultrafine grains that rejuvenates dislocation activities, enabling large plasticity.

Automated summary

This study reports the large plasticity in c-axis compression of submicron magnesium single crystal achieved by a dual-stage deformation. The plastic flow strain-hardens the magnesium crystal to gigapascal level, resulting in the formation of multiple grains. This grain formation rejuvenates dislocation activities and enables large plasticity.