Under the marine atmospheric environment, due to the combined effect of strong solar radiation, high temperature, high humidity and Cl−, the resin macromolecules of polyurethane coating are prone to aging and degradation, resulting in discoloration, powdering and decline in protective performance of the coating surface, which seriously affects the safety of equipment service. Based on this background, many new protection systems have been developed to improve the coating performance. It is very important to quickly evaluate the performance of these coatings in marine environment. The work aims to evaluate the protective performance of "hot sprayed zinc aluminum base fluoropolyurethane heavy protective coating system" and "phosphating film base fluoropolyurethane heavy protective coating system" on Q345 low alloy steel surface in simulated marine environment. Q345 steel was into long squares of 100 mm×35 mm×20 mm as the base materials. The phosphating sample plate and hot sprayed zinc aluminum alloy sample plate were prepared. Then, fluoropolyurethane coating system was sprayed on the surface of the test sample, and scratch samples and non-scratch samples were prepared respectively, and simulated accelerated tests were carried out on the coating samples by laboratory multi-factor combined cycle test. The changes of appearance, gloss and color difference of the coating were analyzed. The corrosion resistance of the coating at the scratch position was compared and analyzed, and the cross-section changes of the hot sprayed zinc aluminum coating before and after the test were analyzed by metallographic method. The aging characteristics and electrochemical properties of the coating were characterized by Fourier transform infrared spectroscopy and electrochemical impedance spectroscopy. After the test, the discoloration grade of two types of fluoropolyurethane protective coating systems was grade 1, the light loss grade was grade 2, and the comprehensive aging performance grade of protective paint film was evaluated as grade 0. The fluoropolyurethane heavy protective coating on the scratch part of the sample of the phosphating film base layer bubbled and rusted, and the unilateral corrosion width was 9.18 mm. The fluoropolyurethane heavy protective coating on the scratch part of the hot sprayed zinc aluminum base layer sample did not bubble, and the unilateral corrosion width was only 2.58 mm. The shape, position and intensity of characteristic infrared peaks of fluoropolyurethane protective coating did not change significantly. The impedance modulus |Z| at 0.01 Hz of the coating system of the phosphating film base layer sample was 2.3×109 Ω·m2 and thermal sprayed zinc aluminum base layer sample was 4.6×109 Ω·cm2. Fluoropolyurethane protective coating has good light aging resistance and corrosion resistance. Compared with the phosphating film base layer, the hot sprayed zinc aluminum base layer can not only improve the durable corrosion resistance of the coating system, but also effectively alleviate the corrosion expansion after the coating is damaged. The fluoropolyurethane heavy protective coating system based on hot sprayed zinc aluminum layer can be used as a metal surface protection technology in marine environment. © 2022, Chongqing Wujiu Periodicals Press. All rights reserved.
