Electrochemical anodic behavior of Ti-6.5Al-1Mo-1V-2Zr in aggressive chloride ions electrolytes

Titanium alloy is hailed as the “space metal” due to its low density, high strength and high-temperature resistance. It is a difficult-to-cut material, and components are often precisely manufactured by electrochemical machining (ECM), with material removed at the atomic level. However, titanium alloys are prone to passivation and pitting during anodic dissolution, and the corrosion mechanism is still unclear. To reveal the formation and breakdown of the passive film, the electrochemical anodic behavior of Ti-6.5Al-1Mo-1 V-2Zr is studied with aggressive chloride ions using polarization curves, electrochemical impedance spectroscopy, Mott–Schottky plot and chronoamperometry. The oxygen elements in pitting and oxidation zones are recorded as 3.08% and 27.81%, and the chloride ions easily pass through the loose and porous layer. The equivalent circuit reveals the structure and resistance value of the passive film, and Mott–Schottky curves show that the passive film is an N-type semiconductor, whose thickness decreases from 2.5 to 1.96 nm with concentration of chloride ions. A small proportion of the processing charge is used for oxidation, while a large proportion of 98.9% is used for anodic dissolution. AFM morphology shows micro-protrusions and micro-depressions, which are similar to the differentiated dissolution of α and β metallographic structures.