Formation of a black anodic coating on alloy AA5052 by using anodizing in a tri-acid environmentally friendly electrolyte

Abstract

For the first time, an organic electrolyte has been created, which allowed the formation of black anodized aluminum (Al) by direct anodizing of alloy AA5052. The electrolyte consists of a mixture of three environmentally friendly acids. The structural and optical properties of black anodic coatings were determined before and after thermal treatment. Total reflection tests of black anodized Al have shown that AA5052 samples have a total reflectance value of 5–7% in the visible (VIS) range. The study of specular reflectance on the angle of incidence of the light at a wavelength of 600 nm has shown that sample AA5052 has the highest angular intensity compared to that of AA1050. Thermal treatment reduced the porosity of alloy AA5052 about 2.5 times, but did not affect its optical properties. Black anodized alloy AA5052 has excellent thermal stability both at 100 °C and 200 °C temperatures, i.e. the total reflectance value did not change by more than 5% in the VIS range. Hence, the developed black anodized coatings are suitable for solar water heating systems.