An oxide film with a thickness of 3-30um is formed on the surface of aluminum or aluminum alloy by artificial methods, so as to improve the corrosion resistance, wear resistance, ability of adsorbing paint and pigment, hardness and insulating properties of aluminum and its alloys.
The basic reason: the anodization of aluminum is essentially the electrolysis of water. After the electrolyte is energized, hydrolysis occurs under the action of current, and oxygen H++eH2↑ is released at the cathode, and electrons are released at the anode, 40H—4e2H20+2O↑. Some of the new oxygen atoms react with the anode aluminum to form anhydrous aluminum oxide film, 2Al3++3O2-AL2O3+ heat.
(1) Anodizing is different from painted film and electroplating film. It hardly peels off and has good adhesion. The oxide film has compressive strength. In the bending test, even if the substrate has been cracked, the anodized film will not fall off. .
(2) The sealing treatment after anodization is an effective measure to improve the protective performance of the membrane layer. The sealing treatment can convert the oxidation of the membrane surface into its hydrate. The most effective method is oxygen anodization and then sealing treatment. The sealing treatment uses The medium used is boiling water, steam, aqueous solution of nickel acetate or cobalt acetate. The oxide film is thermally stable, but it has uniform thickness distribution, mechanical defects such as pores, cracks and structural discontinuities in the film, and impurities in the film, which will reduce the protective performance. Through the oxide film, the corrosion of the base metal will continue to expand, and the generated corrosion products will cause the oxide film to crack, and the corrosion will further deteriorate. The sealing treatment can convert the oxide on the membrane surface into its hydrate, which expands the membrane pores until they are closed, and blocks the passage of the erosive medium for the membrane pores, thereby improving the protective performance of the membrane.
Anodization of aluminum can be carried out in a variety of electrolytes such as sulfuric acid, chromate, phosphate, manganic acid, silicate, carbonate, boric acid, borate, tartrate, oxalic acid, oxalate and others Among the organic acids, sulfuric acid, oxalic acid, chromic acid and boric acid are commonly used in modern times.
The aluminum parts with clean surface are used as the anode, and the lead grid or graphite is used as the cathode, respectively put into the sulfuric acid solution with a mass fraction of 15%-20%, and the electrolysis time is 15-30min by direct current electrolysis according to the alloy grade and film thickness. OK, and finally closed processing.
