The so-called anodizing of aluminum is a Electrolytic oxidation In this process, the surface of aluminum and aluminum alloy is usually transformed into a layer of oxide film, which has protective, decorative and some other functional characteristics. From this definition, anodizing of aluminum only includes generation Anodic oxide film This part of the process. Take metal or alloy parts as anode , using electrolysis To form oxide on its surface film 。 metallic oxide The film changes the surface state and properties, such as surface coloring Corrosion resistance Enhance wear resistance and hardness, protect metal surface, etc. for example Aluminum anodizing Place aluminum and its alloy in corresponding electrolyte (such as sulfuric acid Chromic acid 、 oxalate And so on) as anode to conduct electrolysis under specific conditions and applied current. Anodic aluminum or its alloy is oxidized and formed on the surface alumina Thin layer, its thickness is 5~30 μ m, and the hard anodic oxide film can reach 25~150 μ m. The anodized aluminum or its alloy has improved its hardness and wear resistance, up to 250~500 kg/mm2. It has good heat resistance. The melting point of hard anodic oxide film is up to 2320K, excellent insulation, and breakdown resistance voltage is up to 2000V. It has enhanced its corrosion resistance. It will not be corroded in ω=0.03 NaCl salt spray for thousands of hours. There are a lot of micropores in the thin oxide film, which can absorb various lubricants, and is suitable for manufacturing engine cylinders or other wear-resistant parts; The membrane has strong micropore adsorption capacity and can be colored into various beautiful and beautiful colors. Nonferrous metals or their alloys (such as aluminum, magnesium and their alloys) can be anodized. This method is widely used in mechanical parts, aircraft and automobile parts, precision instruments and radio equipment, daily necessities and architectural decoration. [1] Generally speaking, aluminum or aluminum alloy is used as anode for anode, and lead plate is selected as cathode, and aluminum and lead plate are put together in aqueous solution, which contains sulfuric acid, oxalic acid, chromic acid, etc., for electrolysis to form an oxide film on the surface of aluminum and lead plate. Among these acids, the most extensive is the anodic oxidation with sulfuric acid.
Caused by anodes made of other substances except metals oxidation , also known as "anodizing". 
Oxidation effect of aluminum alloy Protection
Decorative
Insulation
Improve adhesion with organic coating
Improve adhesion with inorganic coating
Other functions under development
Difference between anodic oxidation and conductive oxidation
1) Anodizing is carried out under the condition of high voltage, which is a kind of electricity Chemical reaction process ; However, conductive oxidation (also called chemical oxidation) does not need to be electrified, it only needs to be soaked in liquid medicine. It is a pure chemical reaction. 2) Anodic oxidation takes a long time, often tens of minutes, while conductive oxidation only takes a few tens of seconds.
3) The film formed by anodic oxidation has several microns to dozens of microns, and is hard and wear-resistant; The film formed by conductive oxidation is only 0.01-0.15 μ m, and its wear resistance is not very good, but it can conduct electricity and resist atmospheric corrosion, which is its advantage.
4) The oxide film is originally non-conductive, but because the film formed by conductive oxidation is really thin, it is conductive. [2]
