Zinc-rich epoxy coatings (ZRE) have been widely used in the anti-corrosion of offshore wind power and high-speed trains. However, the utilization rate of Zn powder as sacrificial anode phase in zinc-rich coatings is related to the micro-conductive channels in the coatings. By adding graphene nanosheets (GNP) to zinc-rich epoxy coating (ZRE) to improve the shielding performance of ZRE and the cathodic protection efficiency of zinc powder in the coating, the long-term effect of ZRE coating with 0.5%(mass fraction, the same below) GNP on the protection of carbon steel was studied. Using SEM and optical microscope to characterize the surface micromorphology of the coating and the macromorphology of the metal substrate after simulated seawater immersion. By comparing the characteristic low-frequency impedance |Z|0.01 Hz and the characteristic frequency f-45° with time in the electrochemical impedance of the coating, it was found that GNP could significantly improve the corrosion resistance of ZRE coating. The corrosion development process of ZRE coatings with surface artificial defects in simulated seawater was studied by micro-area electrochemical testing technique (SVET). Results showed that GNP significantly extended the sacrificial anode protection area of Zn powder, improved |Z|0.01 Hz of ZRE with 40% Zn content by an order of magnitude. During 120 h soaking period, GNP/ZRE composite coating provided effective cathodic protection for exposed carbon steel substrate under defect. Further study showed that 0.5% GNP improved the corrosion resistance of 40% ZRE most obviously, followed by 70% ZRE and 10% ZRE. This was because the uniformly dispersed GNP lamellar structure in the ZRE coating could not only significantly improve the physical shielding performance of the ZRE coating, but also activate the sacrificial anode activity of the Zn powder through the GNP-Zn galvanic couple, and strengthen the conductive capacity of the connection between the Zn particles through the bridge effect, thus improving the utilization efficiency of the Zn powder in the coating.
