Exfoliation corrosion of aluminum alloy AA7075 examined by electrochemical impedance spectroscopy

• Published in: Materials and corrosion 2004-01, Vol.55 (1), p.18-23
• Main Authors: Cao, F.-H., Zhang, Z., Li, J.-F., Cheng, Y.-L., Zhang, J.-Q., Cao, C.-N.
• Format: Article
• Language: English
• Subjects: AA7075; Applied sciences; Corrosion; Corrosion environments; Corrosion mechanisms; Electrochemical impedance spectroscopy (EIS); Exact sciences and technology; exfoliation corrosion; Metals. Metallurgy; microstructure
• ISSN: 0947-5117; 1521-4176
• DOI: 10.1002/maco.200303691

A typical aluminum alloy, AA7075, was immersed in the EXCO solution, and its corrosion properties during different immersion time were measured repetitively using electrochemical impedance spectroscopy technique (EIS). The EIS data a were simulated using equivalent circuit with ZView program. The results show that once the exfoliation occurs, the low frequency inductive loop in the Nyquist plot associated with the relaxation phenomenon of reaction intermediates disappears, and the Nyquist plane is mainly composed of two capacitive arcs in the high frequency range and low frequency range respectively. The former originates from the original corroded surface, while the latter from the newly formed interface by exfoliation corrosion (EXCO). With the increased immersion time, the high frequency capacitance arc decreases gradually, while the low frequency capacitance arc increases gradually. From the beginning of immersion up to 9 hours, charge transfer resistance gradually decreases, illustrating the acceleration of the corrosion rate, whereas the proton concentration decreases steeply, indicating the cathodic process is pre‐dominant. Then the corrosion rate decreases gradually corresponding to the exhausting of proton ions. The results also show that the exfoliation corrosion is developed from pitting corrosion through intergranular corrosion to general corrosion at the end.