Electrochemical and SVET Studies on the Typical Polarity Reversal of Cu-304 Stainless Steel Galvanic Couple in Cl−-Containing Solution with Different pH

•The polarity reversal of the Cu-304SS couple in Cl− solution with different pH was investigated.•A typical polarity reversal occurred in the Cu-304SS couple when the solution pH reduced from 2 to 0.•SVET map was used to verify the occurrence of polarity reversal.•The polarity reversal of the Cu-304SS couple is related to formation and dissolution of passive film on 304SS surface.

The typical polarity reversal of the Cu-304 stainless steel galvanic couple (Cu-304SS GC) in Cl−-containing solution with different pH was investigated by open circuit potential (OCP), potentiodynamic polarization, and galvanic current techniques in conjunction with scanning vibrating electrode technique (SVET) and scanning electron microscopy (SEM). The results showed that the change in pH of the solution has a significant effect on the corrosion behavior of 304SS. The typical polarity reversal occurs in Cu-304SS GC in Cl− solution with pH 0, in which the red copper is cathodic to 304SS, while in the solution with pH 6, 4, and 2 the red copper is anodic to 304SS. With the decrease in pH, the 304SS changes from the passive state to the activation state due to the dissolution of the passive film on the surface thereby facilitating the polarity reversal of the Cu-304SS GC.