Grain boundary structure and composition following superplastic deformation of Al-Mg alloys

Evidence for deformation-induced supersaturation of vacancies at grain boundaries is presented for Al-Mg-Mn-based alloys quenched under load from superplastic deformation temperatures. The excess vacancies coalesce into nanoscale cavities that are visible along most grain boundaries following deformation under conditions where grain boundary sliding dominates. Reheating of the samples in-situ in the transmission electron microscope showed that the nanocavities first coalesced and coarsened, then disappeared as the temperature was increased. Localized changes in Mg concentration were also measured as a result of near-boundary vacancy motion. (Author)