Passive film of Ti-6Al-4V alloy laser-welded joint under bending stress at different temperatures

The properties of the passive film on Ti-6Al-4V alloy laser-welded joint under bending stress and stress-free conditions have been investigated at different temperatures (5 and 20°C) in 3.5 wt.% NaCl, and the electrochemical, compositional and morphological analyses have been carried out. It has been found that stress compromises the protectiveness of the passive film and also its re-formation rate, especially at the welded joint (WJ). The film under stressed conditions was thicker than under unstressed conditions but with a non-uniform and loose outer layer. The microstructural inhomogeneity (acicular α ’ martensite and β columnar grains) of the WJ and the low temperature are also key factors that compromise the corrosion resistance, stability, re-formation ability and the uniformity of the passive film. Stressed WJ at low temperature presented the worst quality of the passive film, which may be a potential risk for film degradation and the initiation of stress corrosion in a marine environment.