Superplastic creep of Mg Alloys

Mg alloys become superplastic at elevated temperature as they shift from conventional intragranular plasticity to grain boundary mediated deformation. The mechanisms by which this is achieved and how continuity at grain boundary (GB) triple points is maintained is hotly disputed. Our recent digital image correlation surface deformation maps shed new light on the phenomenon revealing that grains interact to form shear channels linked by new GBs. However, surface measurements cannot tell us whether these are new grains or existing grains emerging at the surface, the surface behaviour is heavily influenced by the unknown grains beneath the surface, and the constraint at the surface is markedly less than in the interior. Here we use a novel combination of in situ DCT, scanning 3D XRD and tri-beam SEM to follow the reorientations, internal stresses and reshaping of the grains in 3D during superplasticity to better understand the cooperative actions we have recently uncovered at the surface.