Accumulative fold-forging (AFF) as a novel severe plastic deformation process to fabricate a high strength ultra-fine grained layered aluminum alloy structure

A novel severe plastic deformation (SPD) process termed accumulative fold forging (AFF) is introduced to fabricate a homogenous ultra-fine grained (UFG) layered metal structure by repetitive folding and forging aluminum alloy foil. The present work studies AFF applied to thin foils of AA8006 Al-Fe-Mn aluminum alloy after 26 folding steps to produce a UFG structure containing 67,108,864 layers across a 2 mm thickness. The structure of the layers and grain refinement are studied using X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM) and scanning-transmission electron microscopy (STEM) analysis. The results indicate a well-bonded inter-layer structure with an average grain size of about 200 nm parallel and 250 nm perpendicular to the forging direction, while dislocation density increased to ~ 7.2 × 1015 m− 2 following AFF. The mechanical strength of the aluminum foil is evaluated in the terms of indentation hardness testing before and after AFF process. The processed UFGed layered material exhibited an average hardness value of ~ 61.5 Vickers as compared to the initial value of ~ 30.4 Vickers for the annealed foil alloy, which indicates an improvement of ~ 100% due to the contributions of grain refinement, work hardening and interfacial strengthening of the bonded layers.