Near-Surface Deformed Layers on Rolled Aluminum Alloys

Near-surface deformed layers, which are characterized by nano-sized fine grains, are generated in aluminum alloys by hot and cold rolling. During the rolling processes, the alloy surface and near-surface regions experience a high level of shear deformation that results in significant microstructure refinement, leading to formation of near-surface deformed layers with microstructures different from that of the underlying bulk alloy. Two types of near-surface deformed layers are observed. Type A is characterized by fine grains with grain boundaries decorated by oxide particles; type B is characterized also by fine grains but with the grain boundaries free of oxide particles. The high levels of shear deformation result in dynamic recrystallization. Together with mechanical alloying, this is responsible for the formation of the near-surface deformed layer. Furthermore, the structure in the near-surface deformed layer can survive the typical annealing process particularly if the grain boundaries are pinned by oxide particles.