Evaluation of corrosion behavior of AA2024 T3 welded by means of FSW

The paper deals with the corrosion behavior of aluminum alloy AA 2024 T3 joined by means of friction stir welding (FSW). Electrochemical impedance spectroscopy (EIS) tests were carried out on four points bending specimens loaded at 80% of Yield Strength, in 35g/L sodium chloride solution. After exposure, the specimens were observed at the optical and scanning electron microscope (SEM) in order to assess corrosion morphologies. The EIS spectra show the initiation of the localized corrosion during first 24 hours of immersion. The modulus of the impedance modifies and a shift towards low frequencies of the bode-phase diagram was noticed over the time. A detrimental effect of FSW process on the corrosion behavior of the alloy due to microstructure modifications is confirmed, but the specimens did not show stress corrosion cracking. An intense intergranular attack was observed in the nugget of welding, close to continuous copper rich precipitates at the border of the recrystallized grains induced by the thermo-mechanical action of the welding process. The precipitates form by the coalescence of sub-micrometric precipitates present in the naturally aged base metal. Intergranular attacks were not observed in heat-affected zone and on base metal – where grain recrystallization does not occur. In these zones, sporadic shallow pits were only observed at large copper rich precipitates.