Additive friction stir deposition (AFSD) is a solid-state additive manufacturing process that demonstrated its capability to repair high strength aluminum alloys without the deleterious effects related to rapid phase changes. This study investigated the influence of heat input on the bonding quality of a lubricant free, twin rod AFSD as deposited repair of simulated damaged 3 mm deep grooves on aluminum alloy 7050 plates to identify processing conditions that yielded improved ductility and tensile strength. Heat input was controlled by a novel temperature control scheme to maintain isothermal depositions at different traverse speeds where slower speeds generated higher heat input (HHI) and faster speeds generated lower heat input (LHI). While both repair conditions produced fully dense deposits that exceeded the mechanical properties of a non-repaired specimen, distinct fracture behavior was observed that affected the resulting mechanical response. The different hardness gradients across the repairs enabled distinct strain localization patterns that shifted from across the entire repair to within the deposit interface during tensile loading for the LHI and HHI repair respectively. The variability of ductility for the HHI condition suggested a sensitivity to processing parameters and underscored the critical role of thermal input in optimizing AFSD repair conditions for improved bonding.
Rojas et al. (Mon,) studied this question.