A Review - Black Oxide Coating on Metal Substrates of Steels, Aluminium, Magnesium and Copper

Aluminium, magnesium, copper, steels and their alloys are generally used in vast applications like automobile, ship, architecture, aerospace due their properties of high strength to weight ratio, good toughness, ease of recycling and good thermal conductivity. In practical applications, surface treatment is required to meet design requirements and also improves the long-term corrosion resistance and functionality. To enhance surface properties electro deposition, sol-gel, anodization and gas phase deposition are causally used in many industries. For achieving better results, one of the alternative coating has been developed such as black coating to modify the metal substrate properties. These black coating can be prepared by conventional method as well as other methods like micro arc oxidation, plasma electrolytic oxidation and pulse micro arc oxidation techniques. Conventional coloring method shows some disadvantages, for instance, poisonous Cr 6+ ions are formed while preparing black oxide coating by conversion of chromium. To avoid such disadvantages, micro arc oxidation, plasma electrolytic oxidation and pulse micro arc oxidation are developed. Based on these techniques, surface properties like long-term corrosion resistance, wear resistance, biocompatibility and decoration are enhanced. Black coatings have high hardness, good bonding with metal substrate, light aging resistance and higher thickness of coating due to strongest absorption ability. This paper mainly focusses the generation of black oxide coating on steel, aluminum, magnesium and copper.