Effects of combined organic and inorganic corrosion inhibitors on the nanostructure cerium based conversion coating performance on AZ31 magnesium alloy: Morphological and corrosion studies

•Cn-Mn-polyvinyl alcohol conversion coating led to more uniform and crack free film deposition.•The corrosion resistance of Ce film was noticeably improved by using combination of polyvinyl alchol and Mn2+ cations.•A synergistic effect between polyvinyl alchol-Mn2+ resulted in Ce film with enhanced morphology and corrosion resistance. Magnesium (Mg) AZ31 samples were chemically treated by a series of room temperature nanostructure cerium based conversion coatings containing Mn(NO3)2·4H2O, Co(NO3)2·6H2O, and polyvinyl alcohol (PVA). The microstructure and corrosion protection properties of different samples were studied by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), electrochemical impedance spectroscopy (EIS) and polarization test in 3.5wt.% NaCl solution. Results demonstrated that the AZ31 Mg alloy sample treated by Ce-Mn-PVA showed the highest corrosion resistance. A denser Ce film with lower crack was precipitated on the sample treated by Ce-Mn-PVA conversion coating.