Construction and corrosion resistance of MAO/COF composite coatings on magnesium alloy

Purpose The purpose of this study MAO/COF composite anti-corrosion coatings is to mitigate the electrochemical corrosion of magnesium alloys and extend their service life. Design/methodology/approach The MAO/COF coating was characterized by scanning electron microscope, energy dispersive spectrometry, X-ray diffraction, Fourier transform infrared spectroscopy and Raman. Optimal process parameters were determined using electrochemical impedance spectroscopy and potentiodynamic polarization. Corrosion resistance and durability of the different coatings were evaluated before and after salt spray exposure via electrochemical testing, and corrosion protection mechanisms were revealed by theoretical calculations. Findings The results indicate that the optimal process parameters obtained via single-factor optimization are 70°C, 6 h and a precursor molar ratio of 1:2. Under these conditions, the MAO/COF coating exhibits superior electrochemical performance compared to other coatings: its charge transfer resistance (Rct) is 3.08 × 105 Ω·cm2, which is two and one orders of magnitude higher than that of AZ91D and MAO, respectively; its corrosion current density (Icorr) is 1.45 × 10–8 A·cm2, three and two orders of magnitude lower than that of AZ91D and MAO, respectively. Meanwhile, quantum mechanical calculations, molecular dynamics simulations and radial distribution function analyses confirm strong interfacial interactions between COF and MAO, indicating good compatibility and stable adsorption within the composite system. Originality/value During the hydrothermal process, COF coatings are in situ grown on the surface of MAO coatings through chemical bonding, forming a dense and highly insulating barrier that effectively blocks corrosive media and significantly enhances the corrosion resistance of magnesium alloys.