Exfoliation corrosion of friction stir welded dissimilar 2024-to-7075 aluminum alloys

Highlights: • Exfoliation corrosion of friction-stir-welded dissimilar 2024-to-7075 is analyzed. • Corrosion behavior of stir zone is similar to the retreating side of base metal. • Intergranular corrosion is prevailing in the stir zone and base metal. • A new relationship between grain size and polarization resistance is proposed. -- Abstract: The objective of this study was to identify the effect of base metal (BM) locations on the corrosion behavior of friction stir welded dissimilar 2024-T351 to 7075-T651 aluminum alloys joints in an EXCO solution. Electron backscatter diffraction (EBSD), transmission electron microscopy (TEM) and high resolution TEM (HRTEM) were conducted to characterize the microstructure evolution of the BMs and stir zones (SZs). Scanning electron microscopy (SEM) was employed to observe the appearance of these corroded zones. Results reveal that the corrosion resistance of SZs is similar to that of the BM positioning in the retreating side (RS), and intergranular corrosion (IGC) is prevailing. The fine recrystallized grains in SZs exhibit more drastic IGC than that of BMs. The discontinuously distributed grain boundary precipitates and precipitate-free zones in the SZ of 2024 reduce the IGC damage of SZ.