Transition of tensile deformation behaviors in ultrafine-grained aluminum

An evident transition of tensile deformation behaviors appeared in commercial purity aluminum as the grain size reduced from micrometer to submicrometer range. The transition grain size decreased as the deformation temperature decreased from room temperature to 77 K. A model was proposed to explain the deformation behaviors in ultrafine-grained (UFG) aluminum. As grain size decreased below a critical value, which may correspond to the cell size present at the applied strain rate and temperature, the mean free path of dislocation was no longer determined by the dislocation structure, but limited by the grain boundaries. This causes an enhancement of dynamic recovery rate, and reduction of hardening rate in UFG metals, leading to the presence of yielding peak, Lüders deformation, and reduced tensile elongation.