Influence of post-treatment on the corrosion resistance of PEO coated AM50B and AM60B Mg alloys

Magnesium alloys are highly reactive and require protection for their successful applications In this work coatings of 10 mu m and 25 mu m nominal thicknesses were prepared by Plasma Electrolytic Oxidation on AM50B and AM60B alloys The effect of subsequent post-PEO treatments such as alkaline phosphate alkaline silicate and sol-gel sealing was studied on coatings with 10 mu m thickness The microstructure and composition of the PEO coatings and post-treated coatings were analysed by Scanning Electron Microscope and Energy Dispersive X ray Spectroscopy Phase analysis of the coatings was carried out using X-ray Diffraction method Potentiodynamic polarization method was used to evaluate the corrosion behaviour of these coatings in 3 5% NaCl solution Electrochemical corrosion results indicated that the sealed PEO coatings of 10 mu m thickness showed better corrosion resistance than the unsealed PEO coatings of 25 mu m thickness The structural surface defects of the PEO coatings were sealed by post-treatments resulting in decreases in surface roughness and open pores Sol-gel post treatment provided the most effective sealing to the PEO coatings (C) 2010 Elsevier B V All rights reserved