Development of a solar reflector coating on AA6061 alloy by plasma electrolytic oxidation

A spacecraft consists of various components which will function with maximum efficiency only when their operating temperature is maintained within certain specified ranges. Passive thermal control elements play an important role in maintaining the temperature of spacecraft components within the specified ranges by suitable selection of thermo-optical properties of the surfaces namely absorptance and emittance. Plasma electrolytic oxidation of AA 6061 is studied as a method to develop a solar reflector coating for space applications. The coatings are developed by making use of a silicate-based electrolyte. The influence of electrolyte composition, average current density, processing time, positive on-time and pulse frequency on the thermo-optical behaviour of the coating is studied. The thickness of the PEO coating is optimized so as to attain thermo-optical properties similar or better than conventional sulphuric acid anodizing. The optimized coating is subjected to adhesion and humidity tests as well as various space simulation tests such as thermal cycling and thermo-vacuum performance tests to evaluate the suitability of the coating as a thermal control surface for space application. Coatings obtained by PEO process and conventional sulphuric acid anodizing are further characterized using SEM, EDX, XPS, XRD and nanoprofilometry to have a comparative study of their morphology, microstructure and composition. Graphical abstract