The fabrication of a conversion film on AZ31 containing carbonate product and evaluation of its corrosion resistance

A carbonate-containing conversion film was fabricated on the surface of AZ31 magnesium alloy to enhance its corrosion resistance by immersion in a CO2 saturated NaOH solution by varying the immersion times (0, 1, 10, 30, and 60 min). Scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) were utilized to investigate the morphology, crystallinity, and composition of the surface, respectively. The corrosion resistance was tested using a 5 wt% NaCl solution and electrochemical analysis was conducted to confirm the influence of the immersion time on the corrosion resistances of AZ31 alloys. The composition of formed film consisting of a magnesium complex was strongly influenced by the immersion time, where the carbonate and aluminum contents on the surface of the samples increased after the immersion treatment. The AZ31 alloy immersed in NaOH for 10 min possessed a suitable conversion coating film with a magnesium complex, consequently leading to the best corrosion resistance.