Increasing the ductility of nanostructured Al and Fe by deformation

Nanostructured Al (fcc) and IF steel (bcc) were produced by accumulative roll-bonding. The structural parameters including morphology, boundary spacing, boundary misorientation and dislocation density were characterized by transmission electron microscopy. Both metals showed a similar structural size scale (200 nm), a formation of a high fraction of high angle boundaries (>15°), the presence of more than 10% of boundaries with misorientation angles less than 2° and a density of interior dislocations. As a result, significant strengthening was achieved in both materials. The two nanostructured metals showed similar but unusual mechanical response to low-temperature annealing treatments which increases the maximum strength and decreases the total elongation. This latter finding has been explored by introducing a cold rolling step following the roll-bonding step. An improvement in ductility has been observed leading to the general suggestion that deformation rather than annealing should be considered when optimizing the properties of nanostructured metals processed by plastic deformation to high strains.