Dislocation boundaries and disclinations formed within the cube-oriented grains during tensile deformation of aluminium

The evolution of dislocation boundaries, comprising a distinct equiaxed cell block structure formed within the cube-oriented grains during tensile straining of an aluminium alloy AA5005, has been investigated in detail using transmission electron microscopy. The observed dislocation substructure displayed a hierarchical character resulting from a gradual development of larger-angle planar dense dislocation walls (DDWs), bounding roughly equiaxed cell blocks, on a background of slightly misoriented tangled cell boundaries. These walls displayed a complex, non-crystallographic character largely governed by the macroscopically imposed deformation geometry. A high degree of freedom in dislocation rearrangement, allowed by the present experimental conditions, resulted in a “random” arrangement of DDWs, in which misorientation vectors were largely scattered and misorientations across consecutive walls displayed a tendency to become more cumulative with increasing strain. The present observations appear to support the dislocation/disclination concept, describing the evolution of DDWs as nucleation, growth and immobilization of partial disclination dipoles.