Abstract
Aluminum alloys with nanocrystalline and ultra-fine grain (UFG) size are of interest because of their high strength - typically more than 30% stronger than conventionally processed alloys. For this study, the microstructure and mechanical behavior of UFG Al 5083 plate, produced by quasi-isostatic forging and rolling of cryomilled powder, has been investigated and compared to coarse-grained Al 5083 - in particular, the ability to strengthen the UFG material further by strain hardening. Plate material was cold rolled up to 50% without cracking. It is found that the UFG structure accommodates dislocations differently than coarse grained materials, but significant strength gains can be achieved. Microstructural evidence shows dislocation forests in UFG Al, while conventional Al forms cells or subgrains. Dislocation densities are quantified in an effort to explain their contribution to the overall strength of the alloy. Analysis of tensile data shows changes in the work hardening rate after cold rolling.