Gradient driven anomalous reversible plasticity in conventional magnesium alloys

In a conventional deformation map, strains in crystalline metals are composed of an elastic part and a plastic part. The latter, primarily contributed by the motion of dislocations which leaves the lattice behind the trace intact, is irreversible. Here we report a significant amount of reversible plastic strain in a coarse-grained gradient magnesium alloy. Plastic torsional strain could be recovered by an amount of 10% when the gradient alloy is subjected to tension. The pre-torsional deformation induced gradient twin lamellas and the consequent back stress by dislocation pileup at the tip of twin lamellas serve as the driving force for the reversed plasticity. We further show that the gradient driven reversible plasticity could be utilized to realize better strength-ductility combination in magnesium based alloys, and is of interest for the engineering practice of those light-weight metals.