Microstructures developed by compressive deformation of coarse grained and ultrafine grained 5083 Al alloys at 77Â K and 298Â K

Compression tests were performed on the well-annealed coarse grained (CG) and the near dislocation-free ultrafine grained (UFG) 5083 Al alloys at 298 K and 77 K. The mechanical behavior of the CG alloy was dominated by the stage III hardening at 298 K and the stage II hardening at 77 K. The microstructure of the CG alloy compressed at 298 K was characterized by well-developed dislocation cells and microbands embedded into those cells, but ill-defined dislocation cells were formed at 77 K. The UFG alloy exhibited the elastic-near perfect plastic behavior at both temperatures. The dislocation cell formation was unlikely to occur in the UFG alloy. Instead, localized shear bands were formed at the onset of plastic deformation at both temperatures as an alternative strain accommodation process. Therefore, the elastic-near perfect plastic behavior of the UFG alloy could be explained by the deformation mode change from the uniform mode associated with the cell formation to the localized mode associated with the shear band formation as the grain size was refined to the UFG regime.