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 Cr6+ 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.

The Effect of Heating Time and Heating Temperatures to Layer Thickness and the Glossiness Level of a Surface in Blackening Coating Process

Metal coating without electrical energy using usually could be the conversion coating technique. One method of the conversion coatings that are widely used in the industrial field is blackening or black oxide coating. Blackening or black oxide coating technique is a chemical conversion process that is formed from the chemical reaction between the iron in ferrous metals by an oxidizing salt to form a layer of magnetite (Fe3O4) thin metal substrates. The metal coating process has a lot of choices to improve the quality of materials from metallic and nonmetallic. This study aims to investigate the effect of the time and the temperature of the heating process of the steel AISI 1015 on the thickness and the value of the glossiness level by the blackening processing technique. The research variables are used various heating process time: 30; 60; and 90 minutes, temperature: 100 °C; 150 ºC and 200 ºC, and other variables are controlled constantly. The workpieces made from a steel metal plate AISI 1015 has a dimension size = 200 x 30 x 3 mm3 in 27 pieces. The experimental method was designed by formation 3 x 3 x 3. It could be revealed the longer the healing process time could increase the thickness of the layer of the workpiece surface. A higher heating temperature could decrease the value of the glossiness level of a metal surface. The surface layer thickness level is found the best in the plating process time about 90 minutes and a temperature of 200ºC with a coating thickness values of 20,27μm. The highest value of the glossiness level is obtained at the highest coating time of 30 minutes at a temperature of 100ºC with the value of the shiny level of about 68.50 GU.