Friction Stir Spot Welding of AA6082-T6 Alloy Sheets with Keyhole Refilling Using Similar Consumable Rod Material: Mechanical Performance and Microstructure Analysis

Achieving keyhole-free joints is critical in Friction Stir Spot Welding (FSSW). This study presents a new approach to eliminate this volumetric defect in AA6082-T6 FSSW sheet joints using a continuous multi-layer Friction Stir Deposition (CMFSD) technique, employing a newly designed AA6082-T6 consumable tool. FSSW was performed at various rotational speeds (350, 550, 750 and 950 rpm) with a 5 s dwell time. Comprehensive macro- and micro-scale evaluations, along with mechanical properties (hardness and tensile-shear load) of the produced joints, were conducted. Additionally, microstructures were examined using Optical Microscopy (OM), while fracture surfaces were analyzed via Scanning Electron Microscopy (SEM). Optimal FSSW conditions were identified at 550 rpm, yielding a stir zone (SZ) hardness of 94.6 ± 1.4 HV and a maximum tensile-shear load of 4.73 ± 0.27 kN. The keyhole was successfully refilled using AA6082-T6 rod material via CMFSD, resulting in a defect-free joint of the same base alloy. Electron Backscattered Diffraction (EBSD) technique was also used to examine the microstructural features. A comparative analysis revealed significant enhancements: the refilled FSSW joints exhibited a 46.5% increase in maximum tensile-shear load and a 66.66% improvement in elongation to failure compared to the highest-FSSW joint performance with the keyhole defect.