Strength and structure in commercial purity aluminium after large strain

Commercial aluminium (AA1050) was deformed to a von Mises effective strain of 10 by equal-channel angular extrusion and subsequently annealed. After annealing, microstructure investigations by electron backscatter diffraction and hardness testing were conducted. Basic microstructure descriptive parameters were extracted from the measurements and used to make proof stress predictions. The hardness data illustrated an initial decrease on annealing followed by an increase to a peak hardness which then decreased again on further annealing. Tensile testing at the same condition revealed a remarkable increase in flow stress compared to the deformed state. No mechanism is concluded, however, it is suggested that hardening by annealing and/or age hardening may be responsible for the effect.