Anticorrosion performance of an eco-friendly coating system including an epoxy tie primer with aluminum tripolyphosphates and a polyurethane topcoat for marine aluminum alloy

The anticorrosion performance of an eco-friendly coating system, including an epoxy tie primer with aluminum tripolyphosphates (ATP) and a polyurethane topcoat for marine aluminum alloy was studied by pull-off adhesion test, electrochemical measurements, and salt spray test. Pull-off adhesion test showed a strong adhesion force between the epoxy tie primer and aluminum alloy substrate. Electrochemical measurements showed that the epoxy tie primer had an excellent corrosion resistance, as also confirmed by the salt spray test. The corrosion protection effect was better when the primer was used in conjunction with polyurethane topcoat. In addition, the compositions of the epoxy tie primer before and after immersion in 3.5 % NaCl solution and corrosion products were characterized by Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD). The excellent anticorrosion performance was mainly attributed to the hydrolysis of the ATP into complex ions, which reacted with metal ions on the surface of the aluminum alloy to form a dense phosphating film. Scanning electron microscope (SEM) and energy-dispersive X-ray spectroscopy (EDS) analysis proved the diffusion of ATP at aluminum alloy/coating interface and chelating reaction between ATP and aluminum alloy substrate.