Microstructure and corrosion resistance of friction stir welded 6061 aluminum alloy joints

This study investigates the effect of friction stir welding (FSW) on the microstructure and corrosion behavior of 6061 aluminum alloy through a comprehensive analysis using optical microscopy, scanning electron microscopy (SEM), and electrochemical techniques. Because of dynamic recrystallization, the FSW process significantly improved the grain structure, reducing it from 95 µm ± 19 µm in the base metal to 9.4 µm ± 7.2 µm in the stir zone. After welding, the coarse Al-Fe-Mn-Si precipitates (∼1.5 µm) in the base metal changed into finer, more evenly distributed Al-Mg precipitates (∼1 µm), according to SEM-EDS analysis. These microstructural modifications enhanced corrosion resistance and decreased galvanic activity. According to weight loss tests, the corrosion rate in the FSWed sample decreased significantly from (4.0 ± 1.9) × 10⁻³ mpy in the base metal to (2.6 ± 0.9) × 10⁻³ mpy. The results of Tafel polarization verified that the welded zone had a lower corrosion current density and a positive shift in corrosion potential from –1000 mV ± 121 mV to –700 mV ± 57 mV. Following both corrosion tests, optical morphology revealed that the FSWed samples had less surface deterioration and pit formation.