New superhydrophobic composite coatings on Mg-Mn-Ce magnesium alloy

A novel combined method for the formation of composite coatings on the Mg-Mn-Ce alloy is developed. Ceramic like matrix was formed on the Mg alloy surface by the plasma electrolytic oxidation. Then the samples were subsequently processed by dip-coating in an alcohol suspension of superdispersed polytetrafluoroethylene and spraying with the tetrafluoroethylene telomers solution. SEM, OSP, and SPM was used to study structure of formed surfaces. It was established by measurements of CA and CAH, as well as surface free energy calculations that formed coatings demonstrate superhydrophobic properties due to the presence of an irregular hierarchical surface structure and low surface free energy of fluoropolymers. The coating preserves its hydrophobic properties after exposure to high and low temperatures, for a long time as well as being in corrosive environments. EDS and XRD data analysis confirmed the presence of organofluorine compounds in the composite layers, including in the form of crystalline polytetrafluoroethylene. Using potentiodynamic polarization test and EIS, it was found that the resulting coatings significantly increase the corrosion resistance of Mg material. These data are also confirmed by salt spray tests for 40 days. Incorporation of fluoropolymers additionally decrease coatings coefficient of friction.