Corrosion Behavior of Dissimilar AA7075–AA2024 Friction Stir Welds: Effects of Tool Configuration, Pass Number, and Post‐Weld Heat Treatment

ABSTRACT The corrosion behavior of dissimilar AA7075‐T651/AA2024‐T3 friction stir welded joints was investigated with respect to tool configuration (TC), welding pass number (WPN), and post‐weld heat treatment (PWHT). SEM/EDS analysis revealed that corrosion was dominated by localized pitting coupled with peripheral intergranular (IG) attack, driven by micro‐galvanic interactions associated with Cu‐rich intermetallic agglomeration within the stir zone (SZ) and adjacent thermo‐mechanically affected zone (TMAZ). TC and WPN influenced corrosion response in a condition‐dependent manner rather than exhibiting a monotonic trend. Potentiodynamic polarization measurements showed corrosion rates ranging from 0.115 to 0.225 mm·yr⁻¹, consistent with pit coalescence and IG connectivity observed after polarization and immersion weight‐loss testing. PWHT improved corrosion resistance in single‐pass joints but intensified localized degradation in dual‐pass conditions. These results demonstrate that corrosion performance in AA7075/AA2024 friction stir welds is governed by the stability of welding‐induced microstructural features, thereby defining limits to the benefits of additional passes and PWHT.