Deformation structures in lightly rolled pure aluminium

Abstract

The dislocation structure of lightly rolled aluminium is free of substantial long-range stresses and thus is a low-energy dislocation structure (LEDS). It consists of ordinary cell walls, dense dislocation walls (DDWs) and microbands (MBs) which are stretched out along DDWs and are composed of small pancake-shaped cells. In one particular sample studied, MBs were found in the orientation of shear bands, although they are not observed macroscopically. Since the DDWs and MBs appear together as if forming one general feature they have been dubbed DDW-MBs. The structure can be explain on two hypotheses: (i) All volume elements enclosed by DDWs, including MBs, are blocks of dislocation cells sharing the same combination of active glide systems which, however, are fewer in number than would be needed to satisfy the Taylor condition fully, for the reason that the rate of work hardening increases with increasing number of simultaneously activated glide systems. (ii) MBs are formed later than the DDWs on which they are situated. They complement the deformation due to the earlier cell blocks towards a better approximation of the Taylor condition. It is considered that MBs assume the orientation of shear bands when the strain in them leads to geometrical softening.