Microstructure and mechanical properties of ARB processed aluminium with different purities

Abstract

99.2% Al (2N-Al), 99.99%Al (4N-Al) and 99.999%Al (5N-Al) were deformed to high strains by accumulative roll-bonding (ARB) at room temperature, and microstructure and mechanical properties were systematically characterized. During the ARB process, original coarse grains were subdivided by deformation-induced high-Angle boundaries into nano-scale grains, where redundant shear strain introduced in the near-surface layers by friction in the non-lubricated rolling signicantly accelerated the formation of nanostructures. It was found that spacing and fraction of high-Angle boundaries can be explained by total equivalent strain taking the effect of shear strain into account. Quite uniform nanostructures dominated by high-Angle boundaries were obtained after 6 cycles of ARB for 2N-Al and 4N-Al, but the boundary spacing was smaller in the 2N-Al than in the 4N-Al. On the other hand, in the case of 5N-Al, recrystallization and grain growth occurred during the roll-bonding process, and nanostructures were not able to be obtained. It was suggested that an increase in the amount of impurities is effective to increase the stability of the nanostructures and to randomize the deformation texture leading to a high fraction of high-Angle boundaries.