The process of using the metal circle plate as the anode, placing it in the electrolyte solution and using electrolysis to form an aluminum oxide film on the surface is called anodizing treatment of the aluminum circle. The principle of aluminum anodization is essentially the principle of water electrolysis.
A prerequisite for the growth of the anodic oxide film is that the electrolyte should have a dissolving effect on the oxide film. However, this does not mean that anodizing can generate oxide films or that the properties of oxide films generated are the same in all electrolytes with dissolution.
The anodised aluminum blanks has many types. According to the current form, the anodizing is divided in to direct current anodizing, alternating current anodizing, and pulse current anodizing. According to the electrolyte, it is divided into: sulfuric acid, oxalic acid, chromic acid, mixed acid and natural color anodizing with sulfoorganic acid as the main solution. Among them, the application of direct current sulfuric acid anodizing method is the most common.
The anodic oxide film consists of two layers, a porous thick outer layer is grown on a dense inner layer with dielectric properties. The latter is called the active layer. The active layer is is composed of anhydrous alumina, which has high hardness and prevents the passage of current. The porous outer layer of the oxide film is mainly composed of amorphous alumina and a small amount of hydrated alumina.
The barrier layer thickness is about 0.03-0.05 μm, which is 0.5%-2.0% of the total film thickness. When the electrolyte is sulfuric acid, the sulfate content in the membrane layer is normally 13%-17%. Most of the excellent properties of oxide films are determined by the thickness and porosity of the porous outer layer, which are closely related to the anodizing conditions.
The anodised aluminum blanks are widely used in mechanical parts, aircraft auto parts, precision instruments and radio equipment, architectural decoration, machine casings, lamps and lighting, consumer electronics, handicrafts, household appliances, interior decoration, signs, furniture, automotive decoration and other industries.