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-SiO₂ 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.