Galvanic corrosion mechanism of Ti-Al coupling: the impact of passive films on the coupling effect

The light metals of titanium and aluminum are often used together, so the risk of galvanic corrosion is inevitable. However, the passive films on both metals will change during the galvanic corrosion process, which affects the coupling effect. Thus, this work aims to investigate the variation of passive films with increasing galvanic corrosion time, and further clarify their impact on galvanic corrosion rate. Motto-Schottky (M-S) curves, electrochemical impedance spectroscope (EIS), zero charge potential and XPS were used to characterize the state of the passive films, potentiodynamic polarization and zero resistance ammeter (ZRA) were utilized to analyze the cathodic and anodic reactions on Ti-Al coupling. The results indicate that during galvanic corrosion process the passive film on cathode titanium alloy is transformed from titanium dioxide to low-valent titanium oxide and titanium hydroxide due to hydrogen adsorption behavior, resulting in the increase of defect density in passive film. The passive film on anode aluminum alloy degrades rapidly in the initial galvanic corrosion stage due to the action of Cl− accumulation by non-electrostatic action, also the cathodic reaction on anode aluminum alloy is relatively high under coupled condition, which plays an important role in the high corrosion rate of anode aluminum alloy.