Effect of lapped sequence on corrosion behavior and mechanism of pure titanium/galvanized steel joint using cold metal transfer joining technology

Titanium/steel joints are widely used in petrochemical, nuclear and aerospace industries. The lapped sequence of dissimilar metal lapped joints can considerably affect their mechanical and corrosion properties. In the study, the microstructure and corrosion behavior of pure titanium/galvanized steel dissimilar cold metal transfer welding joints with different lapped sequences were investigated using microscopic examination, immersion and electrochemical corrosion tests. Pure titanium/galvanized steel joints can be defined as Ti/steel joint (the Ti sheet on top of the steel sheet) or steel/Ti joint (the steel sheet on top of the Ti sheet). The results showed that the corrosion resistance of the Ti/steel joint was poorer than that of the steel/Ti joint in artificial seawater solution because of the formation of larger intermetallics in the weld metal of the Ti/steel joint. Galvanic corrosion occurred in both the Ti/steel and steel/Ti joints. The interface between the galvanized steel base metal and weld metal was the weakest zone in both joints. Moreover, the corrosion mechanisms of the Ti/steel and steel/Ti joints were similar, the reactions were the reduction of oxygen and the evolution of H2 at the cathode. Anodic reactions included the oxidation of metal ions, the formation of TiO2 oxide film and the oxidation of the intermetallics. These findings could contribute to a better understanding of the corrosion behavior of titanium/steel lapped joints under artificial seawater conditions.