Aluminum alloy anodizing process and function

What is aluminum alloy anodizing, what is its process and function? Jiahangaero compiled relevant information, let us explore together. Anodizing refers to the process in which aluminum and its alloys form an oxide film on aluminum products (anodes) under the corresponding electrolyte and specific process conditions under the action of an external current.

The so-called anodizing of aluminum is an electrolytic oxidation 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.

Aluminum alloy anodizing process flow

Aluminum workpiece → hanger → degreasing → water washing → alkali etching → water washing → irradiation → water washing→anodizing→water washing  → deionized water washing → dyeing or electrolytic coloring → water washing → deionized water washing → sealing → water washing → bottom hanger

Aluminum alloy anodizing function

In order to overcome the defects of aluminum and aluminum alloy surface hardness, wear resistance, etc., expand the scope of application, and prolong the service life, surface treatment technology has become an indispensable part of the use of aluminum alloys, and anodizing technology is currently the most widely used.

The aluminum or its alloy of the anode is 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/m㎡, 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.

The process of using aluminum or aluminum alloy products as anodes, placing them in an electrolyte solution for electrification, and using electrolysis to form an aluminum oxide film on the surface is called anodic oxidation treatment of aluminum and aluminum alloys. After anodizing treatment, an oxide film of several microns to hundreds of microns can be formed on the surface of aluminum. Compared with the natural oxide film of aluminum alloy, its corrosion resistance, wear resistance and decoration have been significantly improved and enhanced.

The anodizing of aluminum tubes is generally carried out in an acidic electrolyte with aluminum as the anode. In the electrolysis process, the anion of oxygen reacts with aluminum to form an oxide film. This kind of film is not dense enough when it is first formed. Although it has a certain resistance, the negative oxygen ions in the electrolyte can still reach the aluminum surface and continue to form an oxide film. As the film thickness increases, the electrical resistance also increases, thereby reducing the electrolytic current. At this time, the outer oxide film in contact with the electrolyte is chemically dissolved. When the speed of oxide formation on the aluminum surface gradually balances with the speed of chemical dissolution, the oxide film can reach the thickness under this electrolytic parameter. The outer layer of the anodic oxidation film of aluminum is porous, 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. Non-ferrous 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. It can be dyed to improve its decorative properties. After the oxide film is sealed with hot water, high temperature water vapor or nickel salt, its corrosion resistance and wear resistance can be further improved.

Most of the excellent properties of the anodized film, such as corrosion resistance, wear resistance, adsorption, insulation, etc., are determined by the thickness and porosity of the porous outer layer, but these two are closely related to the anodizing conditions, so it can be By changing the anodizing conditions, the film layer meeting different application requirements can be obtained. Film thickness is a very important performance index of anodized products, and its value directly affects the corrosion resistance, wear resistance, insulation and chemical coloring ability of the film layer.

Because the wear resistance of aluminum alloy is very good after anodizing, it can be used as a necessary process for aviation and aerospace related products. Key points: Anodizing has strict requirements on materials. Different materials have different decorative effects on the surface. The commonly used materials are 6061, 6063, 7075, 2024 and other aluminum alloys. Among them, the relative effect of 2024 is worse, due to the copper content in the material. Different, so 7075 hard anodized is yellow, 6061, 6063 is brown, but there is not much difference between ordinary anodized 6061, 6063, 7075, but 2024 is prone to many gold spots.

Judgment of Common Quality Abnormalities

• 1 Mottling appears on the surface. This kind of abnormality is generally caused by poor metal conditioning or poor material itself. The treatment method is re-heat treatment. or change the material.

• 2 surface appears iridescent. This abnormality is generally caused by the failure of the anode operation. Loose when hanging up, resulting in poor electrical conductivity of the product. The treatment method is to unplug and re-anodize.

• 3 the surface is bruised and severely scratched. This kind of abnormality is generally caused by careless operation during transportation or processing. The treatment method is to unpower, polish and re-power.

• 4 White spots appear on the surface when stained. , This abnormality is generally caused by oil or other impurities in the water during anode operation.

Quality standards

• 1 The film thickness is 5-25um, the hardness is above 200HV, and the color change rate in the sealing test is less than 5%.

• 2 The salt spray test is more than 36 hours, and can reach the CNS standard of 9 or above.

• 3 The appearance should not have bruises, scratches, colorful clouds, etc. There should be no bad phenomena such as hanging points and yellowing on the surface.