Effect of post-rolling after ECAP on deformation behavior of ECAPed commercial Al-Mg alloy at 723Â K

A commercial Al-Mg alloy was subjected to equal channel angular pressing of four passes with and without post-rolling, and the effects of post-rolling on the deformation characteristics of the alloy at 723 K were examined. Post-rolling was found to influence the deformation behavior significantly. The deformation behavior of the alloy processed only by equal channel angular pressing was characterized by (a) localized deformation indicated by severe surface prominence and depression, (b) the strain rate sensitivity of 0.33, and (c) moderate high strain rate superplastic elongations. By contrast, that of the alloy processed by equal channel angular pressing and post-rolling (70% thickness reduction) was manifested by (a) uniform deformation associated with grain boundary sliding throughout the sample, (b) a sigmoidal behavior showing the strain rate sensitivity of 0.45 at the intermediate strain rates in the logarithmic stress-strain rate curve, and (c) very large high strain rate superplastic elongations. Such differences were discussed in terms of the microstructures developed by additional post-rolling after equal channel angular pressing. The above deformation characteristics along with the observation of the surface marker line offsets and the consideration of the dislocation breakaway model revealed that the deformation of the alloy processed only by equal channel angular pressing was governed by dislocation viscous glide, but grain boundary sliding dominated the deformation of the alloy processed by equal channel angular pressing and post-rolling.