The metal or alloy parts are used as anodes, and the surface of the oxide film is formed by electrolysis. The metal oxide film changes the surface state and properties, such as surface coloring, improves corrosion resistance, increases wear resistance and hardness, and protects the metal surface. For example, aluminum anodizing, placing aluminum and its alloys in the corresponding electrolytes, such as sulfuric acid, chromic acid, oxalic acid, etc., as anode, electrolysis under specific conditions and applied currents. The aluminum or its alloy of the anode is oxidized to form a thin layer of alumina on the surface, with a thickness of 5~20 microns and a hard anodic oxide film of up to 60~200 microns. Anodized aluminum or aluminum alloy, improve its hardness and wear resistance, can reach 250 to 500 kg / mm2, good heat resistance, hard anodic oxidation film of high melting point of 2320K, excellent insulation, high breakdown voltage up to 2000V, enhance the corrosion resistance in salt fog by omega = 0.03NaCl thousands of hours without corrosion. The thin layer of oxide film has a large number of micropores, which can adsorb various lubricants, and is suitable for making engine cylinders or other wearable parts. The membrane has strong microporous adsorption ability and can be coloured into various beautiful colors. Nonferrous metals or their alloys, such as aluminum, magnesium and its alloys, can be anodized. This method is widely used in mechanical parts, aircraft, automotive parts, precision instruments and radio equipment, daily necessities and building decoration.
Generally speaking, the anode is aluminum or Aluminum Alloy as anode and cathode is selected to lead, aluminum and lead them in a water solution, there is sulfuric acid, oxalic acid, chromic acid, electrolytic aluminum and lead, make the surface to form an oxide film. The most widespread of these acids is the anodization of sulfuric acid.