A novel sol-gel coating via catechol/lysine polymerization for long-lasting corrosion protection of Mg alloy AZ31

Magnesium alloys are widely used in aerospace and automobile industries because of their lightweight and high strength properties . However, the occurrence of surface corrosion limits their application. Among the protection methods of magnesium alloys, the sol-gel method has received a growing attention recently because of its green economy, high efficiency, and stability. However, the sol-gel method cannot provide corrosion protection for an extended duration in saline solutions. In this study, a novel sol-gel coating via catechol/lysine (CA/Lys) polymerization has been prepared via a facile method and systematically investigated. The CA/Lys co-deposition process was studied by ultraviolet-visible (UV-Vis) spectroscopy. Corrosion performances of the coating were evaluated in aqueous 0.1 M NaCl by electrochemical impedance spectroscopy (EIS) and hydrogen evolution measurements. The experimental results showed that the CA/Lys-modified sol-gel coating provided corrosion protection for up to 18 days, while the unmodified sol-gel coating failed after only 3 days of testing. The polymerized CA/Lys was adsorbed by and then diffused into the sol-gel coating by filling in the macropores or nanopores and the nano-SiO 2 cross-linked network, greatly improving the compactness of the coating. In addition, albeit the thickness of CA/Lys modified coating being only 9 µm, this material was able to provide a long-lasting corrosion protection. This study introduced a novel approach to greatly improve the corrosion resistance of the sol-gel film for magnesium alloys by adopting phenolamines to modify the sol-gel for anticorrosion. This approach can provide a new strategy for Mg alloy corrosion protection.