Damage and strengthening mechanisms in severely deformed commercially pure aluminum: Experiments and modeling

The current investigation presents a breakdown analysis of the elastoplastic behavior of commercially pure aluminum pre-strained via severe plastic deformation (SPD) and tested in tension. The tensile samples selected, owing to their prior SPD, had the gradient microstructure from the fragmentation stage as well as a homogeneous equiaxed structure from the steady-state regime. Except for the regions of low deformation and steady-state of SPD, the microstructures of pre-strained material were largely dominated by the presence of geometrically necessary boundaries. During tensile straining, dislocation strengthening contributed more to the overall material strength in fragmentation stage samples, while grain boundary strengthening played a major role in the steady-state stage samples. The dislocation density evolution rate-based approach predicted a more active role for the dynamic annihilation/recovery events in the SPD material when compared to the fully recrystallized condition. This could explain the drastic drop in tensile elongation of the pre-strained material as well as the enhancement in uniform and post-necking elongation with the gradual increase in the amount of pre-strain. A plastic instability condition based on the dislocation density evolution approach successfully accounted for the observed stable deformation limits in the coarse- and fine-grained material.