Additive friction stir deposition vs. friction surfacing: Comparison of friction stir-based approaches for groove repair of high strength aluminum alloys

Friction stir-based solid-state layer deposition techniques show considerable potential as additive manufacturing approach but also for repair applications. Researchers investigate different techniques, where the layer deposition is mainly based on friction and plastic deformation of a consumable material. The approaches differ in terms of setup and if they utilize a tool to feed the consumable material. This study presents a direct comparison of different friction-based solid-state layer deposition techniques, i.e., additive friction stir deposition (AFSD) and friction surfacing (FS), for the groove repair on the example of high strength aluminum alloys. All deposition strategies present a robust process behavior for groove repair. The AFSD deposits present a sound metallurgical bonding, whereas the FS repair presents some unbonded regions; however, this is significantly improved when hybrid friction diffusion bonding (HFDB) is applied as post-processing technique to the FS deposit. A homogeneous average grain size is obtained in the AFSD deposits, whereas FS deposits present slight variations along layer thickness. The hardness distribution shows that the heat input is higher for AFSD, indicated by larger heat-affected zones in the substrate and lower hardness in the deposited material compared to FS. Overall, both approaches can achieve a successful groove repair with process-characteristic differences.