Characterization of the reactivity of aluminium alloys AA2024-T3 and AA7475-T651 welded by friction stir welding (FSW). ; Caractérisation de la réactivité des alliages d'aluminium AA2024-T3 et AA7475-T651 soudés par friction (FSW). ; Caraterização da reatividade das ligas de aluminio AA2024-T3 E AA7475-T651 soldadas por fricção (FSW).

Friction Stir Welding (FSW) is an efficient process of joining high strength aluminum alloys avoiding defects that are usually created when conventional welding techniques are used. The aircraft industry has shown great interest in this welding method, both for welding of similar or dissimilar alloys. However, this process causes microstructural changes that are dependent on the thermal or thermomechanical conditions applied. Electrical contact between zones of different microstructures, in turn, can result in galvanic coupling. In the present study, FSW was used to join two dissimilar aluminum alloys, AA2024-T3 and AA7475-T651 and the effect of this process on the corrosion resistance of the welded joints and on the microstructure of the alloys was evaluated. For corrosion resistance evaluation, electrochemical tests were used, specifically, open circuit potential measurements (OCP) as a function of time of exposure time to the corrosive environment, polarization tests, and electrochemical impedance spectroscopy, global (EIS) or local (LEIS), in two solutions, either 0.1 M Na2SO4 or 0.1M Na2SO4 + 1 mM NaCl. The electrochemical tests showed galvanic coupling effects in the welded joints. Microstructural characterization was carried out by optical microscopy, scanning electron microscopy, transmission electron microscopy and differencial scanning calorimetry. The welded affected zones showed significant microstructural changes indicated by precipitation and dissolution of precipitates that affect the localized corrosion resistance. Intergranular and exfoliation corrosion resistance of the welded joints were also evaluated and compared to those of unwelded AA2024-T3 and AA7475-T651 alloys. The results showed increased susceptibility of welded joints to these forms of corrosion in comparison with the unwelded alloys with more severe attack associated to the AA7475-T651 alloy. Identification of anodic and cathodic areas due to galvanic coupling in the welded joints was evaluated by a test consisting in depositing a ...