Produce of manganence-type chemical conversion coatings for magnesium alloys and their corrosion resistance.

This paper describes a chromium-free conversion coatings for magnesium alloys. Manganence-type chemical conversion coatings were studies as a corrosion resistance for magnesium alloys. The structure of chemical conversion coatings were investigated by using XRD (X-ray diffraction), XPS (X-ray photoelectron spectroscopy) and GDS (glow discharge spectroscopy). Corrosion resistance of chemical conversion coatings was evaluated in salt immersing spraying. Chemical conversion coatings consist of a film that is composed mainly of MnO2 and partly of Mn2O4, Mn2O3 and MnOOH. It was found that these films formed composit coating. Concentration of KMnO4 in bath for conversion coating formed on magnesium alloy was much lower than that for chromating process. Corrosion resistance of manganence-type chemical conversion coatings was comparable with that for chromating.