Preparation of high absorptance and high emissivity coatings on Mg-Li alloy by plasma electrolytic oxidation

In this work, plasma electrolytic oxidation (PEO) were employed to prepare the thermal control coatings on Mg-Li alloy, which possess great potential in the lightweight of spacecraft. The component, structure and thermal control performances of coatings were controlled by changing reaction time and electrolyte concentration. The results show that all the PEO coatings appeared black in macroscopic scale, owing to the addition of vanadate in electrolyte, and the coatings possessed typical porous structures with some protuberances in micron scale. The main element compositions of coatings were Mg, Si, V, O, Na and P, and most of them existed in form of amorphous phase, resulting from the quenching effect in the process of PEO. The oxide of V mainly existed in the form of +3 valence (V₂O₃), which endow coatings with black appearance. With the increase of possessing time and vanadate concentration, the thickness and roughness of the obtained coatings were improved, and then the absorptance and emissivity presented a growing trend. The optimal conditions were 10 min of reaction time and 10 g l^-1 of vanadate content, and the as-obtained coatings could reach 0.964 of absorptance and 0.951 of emissivity, respectively. Besides, thermal stability test and Tafel curves show that the thermal control coatings also possessed excellent thermal stability and corrosion resistance, which brought the coatings with promising application in aerospace.