Plastic anisotropy in aluminum and copper pre-strained by equal channel angular extrusion

The mechanical response of as-processed equal channel angular extrusion materials is anisotropic, depending on both direction and sense of straining. The stress-strain curves exhibit hardening characteristics different from the usual work hardening responses, e.g., Stages I-IV, expected in annealed fcc metals under monotonic loading. In this work, the anisotropic flow responses of two pure fcc metals, Al and Cu, processed by route Bc are evaluated and compared based on pre-strain level (number of passes), direction of reloading, sense of straining (i.e., compression versus tension), and their propensity to generate subgrain microstructures and to rearrange, should the slip activity change. In most cases, either macroscopic work softening or strain intervals with little to no work hardening are observed. Application of a crystallographically based single-crystal hardening law for strain-path changes [Beyerlein and Tome, Int. J. Plasticity (2007)] incorporated into a visco-plastic self-consistent (VPSC) model supports the hypothesis that suppression of work hardening is due to reversal or cross effects operating at the grain level.