Strain partitioning by recurrent shear localization during equal-channel angular pressing of an AA6060 aluminum alloy

We report on recurrent shear localization by formation of strictly alternating shear and matrix bands during equal-channel angular pressing (ECAP) of a 6000 series aluminum alloy. The strain partitioning process is documented by analyzing the deformation of a grid of indents as well as reconstructing the corresponding flow lines. Interestingly, shear strains of ∼3.6 in the shear bands considerably exceed the conventional maximum shear strain achievable in a single ECAP pass, whereas much lower strains occur in the matrix bands, maintaining on average the macroscopic deformation that is expected for ECA-pressing with a 90° die. Microstructural analysis by electron back-scatter diffraction (EBSD) and scanning transmission electron microscopy documents the different stages of microstructural evolution in shear and matrix bands and confirms the pronounced differences associated with the novel strain partitioning process. Furthermore, an EBSD-based analysis of texture evolution for billets with different orientations with respect to the initial extrusion direction demonstrates the important role that texture softening plays in triggering shear localization in two characteristic orientations as opposed to homogeneous deformation in the third orientation. Shear banding during ECAP is often interpreted in the light of failure mechanisms and cracking; the present study demonstrates that stable strain partitioning facilitates the fabrication of bulk laminated materials by ECAP.