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The so-called anodizing of aluminum is an electrolytic anodizing process in which the surface of aluminum and aluminum alloys is usually converted into an oxide film, which has protective, decorative and some other functional properties. The anodizing of aluminum starting from this definition only includes the process of forming anodic oxide film.
The metal or alloy parts are used as the anode, and the oxide film is formed on the surface by electrolysis. The metal oxide film changes the surface state and properties, such as surface coloring, improves corrosion resistance, enhances wear resistance and hardness, and protects the metal surface. For example, aluminum anodizing, aluminum and its alloys are placed in the corresponding electrolyte (such as sulfuric acid, chromic acid, oxalic acid, etc.) as the anode, and electrolysis is carried out under specific conditions and external current. The aluminum or its alloys of the anode are oxidized, and a thin layer of aluminum oxide is formed on the surface, the thickness of which is 5-30 microns, and the hard anodic oxide film can reach 25-150 microns. Anodized aluminum or its alloys improve its hardness and wear resistance, up to 250-500 kg/mm2, good heat resistance, hard anodized film melting point up to 2320K, excellent insulation, impact resistance The breakdown voltage is as high as 2000V, which enhances the corrosion resistance and does not corrode for thousands of hours in ω=0.03NaCl salt spray. There are a large number of micropores in the oxide film thin layer, which can absorb various lubricants, and is suitable for manufacturing engine cylinders or other wear-resistant parts; the film micropores have strong adsorption capacity and can be colored into various beautiful and bright colors. Nonferrous metals or their alloys (such as aluminum, magnesium and their alloys, etc.) can be anodized. This method is widely used in mechanical parts, aircraft and auto parts, precision instruments and radio equipment, daily necessities and architectural decoration. [1]
Generally speaking, the anode is made of aluminum or aluminum alloy as the anode, and the cathode is the lead plate. Put the aluminum and the lead plate together in the aqueous solution, which contains sulfuric acid, oxalic acid, chromic acid, etc. form an oxide film on the surface. Of these acids, the most widespread is anodizing with sulfuric acid.
