Impact of tool-axis offset on corrosion performance of groove-repaired AA6061 with SiC via friction stir welding

The corrosion behavior of the repaired surface-cracked Al6061-T6 developed by Friction Stir Welding (FSW) was investigated in this study. Square surface grooves (2 × 2 mm) were machined to simulate cracks and packed with AA6061-T6 rod plus SiC nanoparticles prior to the FSW. Five conditions were examined: base metal (BM), FSW without groove/filler (T1), and three repaired plates with the tool axis positioned centrally over the groove (T2), +0.5 D offset toward the advancing side (T3), and +1.0 D offset toward the advancing side (T4). Macro/Microstructure metallography, scanning electron microscopy (SEM), potentiodynamic polarization (PDP), and electrochemical impedance spectroscopy (EIS) characterization were conducted on repaired samples exposed to a corrosive chloride solution. It was observed from the EIS results that the anticorrosion performance of all welded states outperformed the BM sample. The electrochemical results also revealed that the overall corrosion ranking was T1 ≫ T2 ≈ T4 > T3 ≫ BM. Microstructurally, all welded SZs were noticed to contain fine equiaxed grains and dispersed SiC/fragmented constituents; however, tool-offset altered the material flow where zero offset (T2) yielded uniform, and defect-free bands; on the other hand +0.5 D offset (T3) produced particle-rich stringers/wormhole precursors, while +1.0 D offset (T4) intensified onion-ring banding. SEM analyses mirrored these features, in which sparse and shallow pits were observed for T1, isolated pits for T2, and band-localized pits with porous products for T3/T4, which can also be used to explain the anticorrosion trends of all samples obtained from the electrochemical results. Overall, this study explores the feasibility of the FSW tool offset to repair SiC-packed surface cracks and its effect on the corrosion response of the repaired joints.