Multiscale electrochemical study of welded al alloys joined by friction stir welding

Abstract

Friction stir welding (FSW) is an efficient way to join high strength aluminum alloys. However, FSW generates different microstructural areas in contact that may give rise to galvanic couplings, affecting the corrosion resistance of the assembly. In the present work, a multiscale electrochemical study of the 7475-T651 and 2024-T3 aluminum alloys butt-joined by FSW was carried out.Much lower impedances were associated with the FSW affected zones compared to the two aluminum base metals tested individually. Corrosion of the welded system resulted in the establishment of galvanic coupling, shown by local electrochemical impedance spectroscopy (LEIS) measurements, at which the AA7475 behaves anodically with respect to the AA2024. A Zn deposit was observed on the intermetallic particles of the AA2024 after 24 h of immersion in the electrolyte resulting from the galvanic coupling, which seems to reduce the galvanic coupling effects. Such a behavior in combination with LEIS results allowed a description of the galvanic coupling development between two different aluminum alloys (AA2024-T3 and AA7475-T761) butt-welded by FSW as a function of time from the early stage of immersion.