Feasibility Study on the Production of Fillet Welds with Defined Throat Thickness Using Wire-Based Corner Fillet Friction Stir Welding

Friction stir welding of T- and corner-joint configurations is challenging due to restricted tool accessibility, complex material flow and the limited availability of material for the formation of load-bearing fillet-weld geometries. This study introduces wire-based corner fillet friction stir welding (W-CFFSW), a solid-state joining process in which filler wire is continuously transported, plasticised and supplied into the internal corner region through a rotating extrusion screw. A stationary shoulder confines and shapes the deposited material, enabling the formation of fillet welds with a defined throat thickness. Single- and double-sided fillet-weld geometries were produced in 3.0 mm thick EN AW-6082-T6 sheets using EN AW-6082 filler wire. A throat thickness of 4.5 mm was successfully generated by adapting the supplied filler volume to the targeted fillet geometry. Metallographic investigations revealed characteristic FSW microstructural zones and pronounced material flow within the weld nugget zone, while no macroscopic pores or voids were observed in the investigated cross-sections. The hardness distribution exhibited the characteristic W-shaped profile of precipitation-hardenable aluminium alloys. Bending tests showed no separation of the bonding interfaces, with cracking occurring in the adjacent sheet material rather than within the fillet welds. Tensile strengths of 231.55 MPa and 217.49 MPa were achieved for stiffener- and stringer-loaded specimens, corresponding to joint efficiencies of 66 % and 62 %, respectively. The results demonstrate that W-CFFSW enables the controlled addition of filler material to produce mechanically load-bearing fillet welds with a defined throat thickness and represents a promising alternative to existing friction-stir-based T- and corner-joint processes.