The so-called aluminum anodizing process is an electrolytic oxidation process. In this process, the surfaces of aluminum and aluminum alloys are usually converted into an oxide film, which has protective, decorative and some other functional characteristics. From this definition, the anodization of aluminum includes only part of the process of generating anodized film.

The metal or alloy product is used as an anode, and an oxide film is formed on the surface by electrolysis. The metal oxide film changes the surface state and performance, such as surface coloring, improves corrosion resistance, enhances wear resistance and hardness, and protects the metal surface. For example, aluminum is anodized, and aluminum and its alloys are placed in corresponding electrolytes (such as sulfuric acid, chromic acid, oxalic acid, etc.) as anodes, and electrolysis is performed under specific conditions and applied current. The aluminum or its alloy of the anode is oxidized, and a thin layer of alumina is formed on the surface, the thickness of which is 5-30 microns, and the hard anodized film can reach 25-150 microns. Anodized aluminum or its alloy improves 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 penetration voltage is up to 2000V, which enhances the corrosion resistance, and does not corrode in ω = 0.03NaCl salt spray for thousands of hours. The thin layer of the oxide film has a large number of micropores, which can absorb various lubricants, and is suitable for manufacturing engine cylinders or other wear-resistant parts; the strong absorption capacity of the film micropores can be colored into various beautiful and beautiful colors. Non-ferrous metals or their alloys (such as aluminum, magnesium and their alloys) can be anodized. This method is widely used in mechanical parts, aircraft and auto parts, precision instruments and radio equipment, daily necessities and building decoration.

Generally speaking, the anode is aluminum or aluminum alloy as the anode, and the cathode is selected from a lead plate. The aluminum and the lead plate are placed together in an aqueous solution. There are sulfuric acid, oxalic acid, chromic acid, etc. for electrolysis to make the aluminum and the lead plate. An oxide film is formed on the surface. Among these acids, the most widespread is anodization with sulfuric acid.

The parameters of anodizing process should pay attention to the following points:

1. Sulfuric acid concentration. Changing the concentration of sulfuric acid will have a certain effect on the thickness of the barrier layer of the oxide film, the conductivity of the electrolyte and the dissolution of the oxide film, the corrosion resistance and wear resistance of the oxide film, and the sealing quality of the subsequent treatment. The concentration of sulfuric acid is high, which has a great effect on the dissolution of the oxide film. The taper of the pores of the oxide film is large, and the outer pore diameter is increased, which makes the sealing difficult.

2. Bath temperature. During the anodizing process, part of the electrical energy will be converted into heat, so the bath must be cooled to reduce the temperature in order to maintain a suitable temperature range. As the temperature increases, the film quality to metal loss ratio decreases significantly, and the outer hardness of the film is lower. Such films are prone to "pulverization".

3. Oxidation current density. The oxidation current density is directly related to production efficiency. When a higher oxidation current density is used, the time required to obtain an oxide film of a predetermined thickness can be shortened, the production efficiency is high, but the capacity of the power supply is large. And when the current density is too large, it will break down the barrier layer of the oxide film and "burn" the workpiece.

4. Stir the bath. In order to make the temperature and concentration of the anodizing bath uniform, especially when a large current density is adopted, a large amount of heat in the vicinity of the oxide film is taken away in time, and the bath is generally stirred during the anodizing process. There are two ways to stir the bath. One is to stir with oil-free air. The second is to circulate and stir with an acid pump. It is worth mentioning here that, as mentioned above, huge heat is generated during the anodizing process. At this time, part of the bath liquid will be evaporated into steam. It is recommended to add the ht402 oxidation tank acid mist inhibitor during oxidation, which will not affect the oxidation and avoid personal injury and cost.

5. Oxidation time. The control of oxidation time is more troublesome because it is determined according to the requirements of sulfuric acid concentration, bath temperature, current density, and aluminum oxide workpiece thickness and performance of the oxide film.