PREPARATION OF PEO COATINGS ON AZ31 MAGNESIUM ALLOY IN THE PRESENCE OF HUMIC ACID

Magnesium materials are desirable for surface treatment because of their low corrosion resistance. The preparation of coatings on AZ31 alloy by plasma electrolytic oxidation (PEO) in a bath with and without humic acid was investigated. The coatings were characterized using a scanning electron microscope (SEM) with energy dispersive X-ray spectroscopy (EDS) and Fourier transform infrared spectroscopy (FTIR). The corrosion properties were tested using the potentiodynamic polarization method in 0.15 M NaCl. The results show that the PEO coatings had significantly higher corrosion resistance than the AZ31 alloy. The PEO coating prepared in the presence of 5 mg/l humic acid (10 min deposition) appeared to have slightly better corrosion resistance than the PEO coating prepared in the absence of humic acid.