Influence of chloride ion concentration on the electrochemical corrosion behaviour of plasma electrolytic oxidation coated AM50 magnesium alloy

• Published in: Electrochimica acta Vol. 55; no. 22; pp. 6802 - 6811
• Main Authors: Liang, J., Srinivasan, P. Bala, Blawert, C., Dietzel, W.
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 01.09.2010; Elsevier
• Subjects: Applied sciences; Chloride ion concentration; Chlorides; Coating; Corrosion; Corrosion mechanisms; Damage; Degradation mechanism; Electrochemical corrosion; Electrochemical impedance spectroscopy; Exact sciences and technology; Ion concentration; Magnesium; Magnesium alloy; Magnesium base alloys; Metals. Metallurgy; Microstructure; Plasma electrolytic oxidation; Protective coatings; Degradation mechanism; Electrochemical corrosion; Plasma electrolytic oxidation; Microstructure; Chloride ion concentration; Magnesium alloy; Scanning electron microscopy; Plasma assisted processing; Mechanism; Surface treatment; Surface structure; Degradation; Chlorides; Morphology; Concentration effect; Oxidation; Electrochemical reaction; Electrochemical impedance spectroscopy
• ISSN: 0013-4686; 1873-3859
• DOI: 10.1016/j.electacta.2010.05.087

The electrochemical degradation of a silicate- and a phosphate-based plasma electrolytic oxidation (PEO) coated AM50 magnesium alloy obtained using a pulsed DC power supply was investigated using potentiodynamic polarisation and electrochemical impedance spectroscopy (EIS) in NaCl solutions of different chloride ion concentrations viz., 0.01 M, 0.1 M, 0.5 M and 1 M. The surface of the PEO coated specimens after 50 h of immersion/EIS testing was examined by optical microscopy and scanning electron microscopy. The results showed that the corrosion deterioration of PEO coated magnesium alloy in NaCl solutions was significantly influenced by chloride ion concentration. The silicate-based coating was found to offer a superior corrosion resistance to the magnesium substrate than the phosphate-based coatings in lower chloride ion concentration NaCl solutions (0.01 M and 0.1 M NaCl). On the other hand both these PEO coatings were found to be highly susceptible to localized damage, and could not provide an effective corrosion protection to Mg alloy substrate in solutions containing higher chloride concentrations (0.5 M and 1 M). The extent of localized damage was observed to be more with increase in chloride concentration in both the cases.