Application Fields of Aluminum Anodizing

It is well known that aluminum and its alloys oxidize in the air. The naturally formed oxide film on the surface of aluminum is amorphous, which can cause the aluminum metal surface to lose its original luster. Although this natural oxide film can slightly passivate the aluminum metal surface, it is very thin, about 4-5nm, and has high porosity and poor mechanical properties. It cannot effectively prevent further corrosion of aluminum metal by various media in the atmosphere.
After anodizing treatment, a dense film layer (ranging from tens of micrometers to even hundreds of micrometers) can be obtained on the surface of aluminum and its alloys, which is much thicker than the natural oxide film. This layer of artificial oxide film is further sealed, and the amorphous oxide film is transformed into a crystalline oxide film. The pores are also sealed, so that the surface luster of the metal can remain unchanged for a long time, and the corrosion resistance and mechanical strength are improved. After dyeing, a decorative appearance can also be obtained. Due to the many characteristics of aluminum and its alloy products after anodizing, the aluminum anodizing process is widely used in the surface treatment of aluminum products. The applications in industry can be roughly divided into the following categories.
(1) Prevention of product corrosion: Due to the appropriate sealing treatment of the film layer obtained by anodizing, it has good stability in the atmosphere. Whether obtained from sulfuric acid solution, oxalic acid solution, or chromic acid solution in normal processes, the oxide film has excellent corrosion resistance, such as daily aluminum pots, kettles, washing machine liners, etc. The chromic acid oxidation method is particularly suitable for aluminum welded and riveted parts.
(2) Protection and decoration: On the surface of an oxide film with high transparency, the oxide film has the characteristic of adsorbing various organic or inorganic pigments. Various bright and bright colors and patterns can be obtained on the oxide film. In addition, in recent years, many new technologies have emerged, such as multiple coloring in one oxidation, fireworks patterns, wood grain patterns, oxide offset transfer printing, porcelain oxidation, etc., making the appearance of aluminum more beautiful and pleasing to the eye, This colored film is both a decorative layer and an anti-corrosion layer, such as a lighter. Gold pens and handicrafts.
(3) As a hard wear-resistant layer: In sulfuric acid or oxalic acid solutions, a thick and hard film layer can be obtained by adjusting the process conditions of anodizing. The pores and absorption properties of the film layer are used to store the selected oil, which is effectively applied to working conditions under frictional conditions. At the same time, it has characteristics of lubrication and wear resistance, such as engine cylinders, pistons, etc. of automobiles and tractors.
(4) As an insulation layer for electricity: The oxide film layer of aluminum and its alloys has the characteristic of high resistance, and the thickness of the film layer is directly proportional to the resistance. This characteristic has practical significance as an insulation layer for electricity, and can be used as a dielectric for capacitors. Aluminum oxide skin can also be used as the outer cover of cables, replacing rubber and plastic skin as an insulation layer on its surface. It is relatively popular abroad, and its breakdown voltage is 441V when the film thickness is 27.5um. If phenolic resin is used as a filling material for membrane pores, its breakdown voltage can be increased by two times. In oxalic acid solution, as the film thickness increases, a high-quality insulation layer with a resistance of 200fl and a breakdown voltage of 980V can be obtained. Of course, this feature can be used not only for wires, but also for other electrical appliances and other aspects.
(5) Used as the bottom layer for spray painting and electroplating: Due to the porous nature and good adsorption ability of the oxide film layer, it has good adhesion with the paint film and organic film, and can be used as the bottom layer for spray painting. The film layer anodized with phosphoric acid can serve as the bottom layer for electroplating on aluminum.
(6) Used in modern architecture: Due to the introduction of aluminum alloy electrolytic coloring technology, the application of electrolytic coloring in building aluminum profiles in China has been increasing in recent years. It not only has bronze, black, red and other colors suitable for building colors, but also has better wear resistance than conventional oxidation. It is particularly worth mentioning that it has excellent sun resistance and does not fade in the atmosphere after more than 20 years of exposure to sunlight and night exposure, which is incomparable to the oxidation coloring method. Aluminum profiles oxidized by electrolytic coloring method can not only be used for building doors and windows, but also be particularly suitable for use as store counters, shelves, etc.