Corrosion Resistance Behavior of Zinc Substrate Treated with Rare Earth Salt Passivation

A composite passivation film consisting of rare-earth cerium and lanthanum oxides was prepared on the zinc substrate from a passivation solution containing the cerium and lanthanum nitrate. The passivation film exhibits a dense surface feature with a hill -like growth structure. The composition, valence group, and functional group of the passivation film was analyzed by EDS, XPS, and FTIR, and the results showed that the passivation film was mainly composed of cerium and lanthanum oxides. Corrosion evaluation experiments from the electrochemical analysis involving the potentiodynamic polarization and electrochemical impedance spectroscopy and copper sulfate spot test showed that the rare-earth passivation film has a good corrosion resistance, which is comparable to that of the conventional trivalent chromate passivation film. The comprehensive analysis based on the electrochemical behavior, morphology, and composition of the passivation film after immersion also further illuminated that this composite passivation film has a good self-healing and long-term stability.