A novel rolling procedure to enhance ECAP processed ultrafine grained materials

The present study proposes a novel approach to rolling in order to achieve further microstructure modification and mechanical properties improvement of already severely deformed materials. Commercially pure aluminium was subjected to the combined, two stages, heavy strain processes. First, samples were deformed using multi-turn equal channel angular pressing. Five passes of two-turn channel resulted in high strain level, which equaled 11.5. After such a deformation, the microstructure consists of ultrafine grained structure with the fraction of high angle grain boundaries equaled 61%. Then, the second plastic forming process was applied i.e. multi rotational flat rolling. Proposed multipass rolling is based on maintaining a square cross-section of the workpiece. Rolling of severely deformed sample with the thickness reduction of 25% resulted in the improvement in mechanical strength about 15%. It is caused by the increased fraction of high angle grain boundaries up to 75%, while differences in average grain/subgrain size between samples are insignificant.