Study on the Corrosion Behavior of Resistance Spot Welded Dissimilar 2195/5A06 Joints

Four-mm-thick AA2195-T8 aluminum-lithium (Al-Li) alloy and 2 mm thick 5A06 aluminum (Al) alloy were welded by resistance spot welding. Microstructure observation showed that the fusion zone was composed of all equiaxed spherical grains, and theta ' (Al2Cu) phases precipitated were mainly distributed at the grain boundary. The corrosion behavior of resistance spot welded 2195 Al-Li alloy and 5A06 alloy joints was revealed via immersion corrosion and electrochemical corrosion. The immersion test showed that the corrosion behavior of the heat-affected zone of 5A06 and fusion zone was pitting corrosion and intergranular corrosion, other regions of the joint were mainly pitting corrosion. It was found that the oxygen content of fusion zone increased with increasing immersion time. In addition, the oxide film initially formed and finally broken, which resulted from the potential difference between the Al matrix and the grain boundaries. The electrochemical corrosion results showed that the fusion zone exhibited the highest corrosion current density. The higher corrosion rate and corrosion depth of the fusion zone were correlated with Cu element segregation at the grain boundary.