Study of black protective-decorative nanocomposite anodic coatings on the surface of AMg5 aluminum alloy

A widely used nanocomposite coating is a porous anodic alumina colored by particles of metals or their compounds deposited into the pores. The insertion of light-scattering nanosized particles into the pores changes the optical properties of the anodic oxide, whereas the immobilization of metal nanoparticles in pores ensures their corrosion resistance. We present the results of studying black protective and decorative coatings on the surface of AMg5 aluminum alloy. The surface morphology of the samples was analyzed using atomic force microscopy, and the electrophysical properties were monitored by electrochemical impedance spectroscopy (EIS). The growth kinetics of the anodic coating has been studied, and optimal conditions for the formation of a regularly porous oxide coating 10 – 12 μm thick with a regular pore diameter of 15 ± 5 nm on the alloy surface were determined. It is shown that subsequent electrochemical coloring for 15 min makes it possible to obtain a black color of the coatings due to the deposition of Cu and/or CuO nanoparticles into the pores. Simulation of electrical equivalent circuits makes it possible to separate and calculate the electrical parameters corresponding to different layers and elucidate their regular changes after coloring and hydrothermal treatment. The high corrosion resistance of electrochemically colored anodized alloy samples subjected to hydrothermal treatment has been revealed. The results obtained can be used in the application of protective and decorative anodic coatings for the manufacture, for example, of solar panels due to the high absorption and low reflectivity of black coatings.