Corrosion mechanism of the Ti–6Al–4V/AA6061 dissimilar metal CMT welded joint

Ti–Al composites are increasingly used in aviation for their lightweight, strength, and corrosion resistance. This study investigates the microstructural influence on the corrosion performance of Ti/Al Cold Metal Transfer welded joints by X-ray Photoelectron Ppectroscopy (XPS), Local Electrochemical Impedance Spectroscopy (LEIS), and Scanning Kelvin Probe Force Microscopy (SKPFM). The results indicate that, due to the inhomogeneity of the microstructure, the corrosion primarily occurs in the aluminum base metal (Al-BM) and the weld metal (WM), causing pitting and accumulation of corrosion products (Al₂O₃, Al(OH)₃, and AlO(OH)). The Ti (Al, Si)₃ IMC layer disrupted the continuity of the interfacial microstructure in the Ti/WM region. Due to the synergistic effect of both macroscopic and microscopic galvanic corrosion, a strong coupled current density was generated at the interface, leading to severe corrosion. Additionally, the experimental results were also mathematically validated using general theoretical expressions for potential and current. The corrosion process of the WM and Al-BM regions consists of three stages: passive film formation, selective dissolution, and depth propagation. These findings improve our understanding of Ti/Al joint corrosion behavior and provide theoretical support for improving corrosion resistance and extending service life.