Corrosion protection investigations of carbon dots and polydopamine composite coating on magnesium alloy

A composite coating of nitrogen-doped carbon dots (NCDs) and polydopamine (PDA) was prepared on magnesium alloy by combining electrodeposition with dip coating methods. The microstructure of the NCDs/PDA composite coating, including composition, surface morphology, and crystalline structure, is characterized by Raman spectroscopy, scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy, respectively. The corrosion protection performances of the composite coating are evaluated by potentiodynamic polarization tests, electrochemical impedance spectroscopy, and salt spray tests. The effect of the particle size of the NCDs on the corrosion performance is also investigated. The results show that the corrosion performance of the NCDs coatings are enhanced with the increase of the particle sizes. Furthermore, an obvious self-healing performance is observed on the surface of the NCDs/PDA composite coating. These results indicate that NCDs/PDA composite coating can improve the corrosion performance of the Mg alloy, and open a new design direction for the protective coating of metallic materials.