Deformation behavior of a cold-rolled 7075 Al alloy sheet containing small sub-grains with wide low-angle boundaries

An alloy (called I-7075 Al alloy) was prepared by introducing decomposed oxygen atoms from nano-sized ZnO particles into a conventional 7075 Al alloy using a non-metallic alloying method. After solidification, sub-grains with a size of smaller than 1 μ m were developed by the formation of wide Al–O nanoclusters (∼40 nm in width) appeared along the sub-grain boundaries. The clusters contained many pre-existing dislocations to accommodate the lattice mismatch between the matrix and the Al–O nanocluster, and served as dislocation cells during plastic deformation, thereby enhancing the dislocation storage capacity. Thus, the homogenized I-7075 Al alloy exhibited a high elongation of approximately 20%, which can increase the total cold rolling reduction to 90%. The large cold rolling capacity reduces the recrystallized grain size of the I-7075 Al alloy sheet to 20.1 μm, which is smaller than the hot-rolled 7075 Al alloy sheet with a recrystallized grain size of 34.2 μm. Owing to the role of the Al–O nanoclusters during plastic deformation, the elongation of the recrystallized and T6 aged I-7075 Al alloy sheets increased by approximately 40% and 50%, respectively, compared to those of the hot-rolled 7075 Al alloy sheet.