Improved corrosion resistance of EP coating on Mg alloy through GO hybridization and silica-based superhydrophobic surface

Epoxy resin (EP) coating has high hydrophilicity and poor long-term corrosion resistance. In order to improve its protection ability, an EP-graphene oxide (GO)/SiO2 multifunctional coating is fabricated on Mg-Zn-Ca alloy in this study, through a spin/spray assisted self-assembly technique. The morphologies and microstructures of the coated samples were observed using scanning electron microscopy (SEM), Fourier infrared spectrometer (FTIR) and atomic force microscope (AFM). Hydrophobicity and self-cleaning property of the composite coating were tested by an optical contact angle meter and black graphite powders. The stability of the superhydrophobic surface was tested by rubbing with sandpaper and immersing in corrosion solution. The corrosion resistance of coated samples was tested in 3.5 % NaCl solution using electrochemical impedance spectroscopy (EIS). The GO sheets are uniformly dispersed in EP coating. EP-GO acts as a dense bottom layer, effectively promoting its adhesion with the superhydrophobic SiO2 coating, and the water contact angle (WCA) values range from 158° to 168°. After stability testing, the WCA value of the superhydrophobic coating remains at a high level (115°–155°). The Rct of this composite coating was remarkably increased to 1.0 × 1022 Ω/cm2, implying that the corrosion resistance was improved by eighteen orders of magnitude compared to bare substrate. These results show that the combination of the labyrinth effect and the hydrophobic surface extend the corrosion path and reduce the contact area of the corrosion solution with the coating, which strengthens the barrier effect of the composite coating. The composite coating exhibits superior corrosion resistance durability and self-cleaning property.