Anodized Anodic Structure Of Aluminum

1) Anodic oxide film structure Anodic oxide film is composed of two layers, the outer layer is called porous layer, thick, loose porous, low resistance. The inner layer is called the barrier layer (also known as the active layer), which is thin, dense and has high resistance. The porous outer layer grows on top of a dense inner layer with dielectric properties. In general, the anodic oxide film is a series of hexagonal columns, each column has a star-shaped hole filled with solution, the shape of a honeycomb structure, the hole wall thickness is twice the diameter of the pore.

(1) Barrier layer Barrier layer is composed of anhydrous AI2O3, thin and dense, with high hardness and the effect of preventing the passage of current. (2) Porous outer oxide film Porous outer layer is mainly composed of amorphous AI2O3 and a small amount of r-AI2O3.H2O also contains electrolyte anion.

The pore size of the oxide film is between 100nm and 200nm, the thickness of the oxide film is about 10 microns, the porosity is about 20%, and the pore distance is between 300 nm and 500nm. The cross section of the oxide film shows that the oxide film hole is basically tubular structure, and the dissolution reaction of the oxide film is basically at the bottom of the hole. And the general sulfuric acid DC anodic oxidation film aperture is about 20nm, if it is 12 micron oxide film, it is how deep the fine tubular structure ah! Assuming this is a 1m diameter well, it will be 600m deep.

Most of the excellent properties of oxide film, such as corrosion resistance, wear resistance, adsorption, insulation and other properties are determined by the thickness and porosity of the porous outer layer. However, these two are closely related to the anodizing conditions, so the anodizing conditions can be changed to meet the requirements of different use of the film. Film thickness is a very important performance indicator of anodized products, and its value directly affects the corrosion resistance, wear resistance, insulation and chemical coloring ability of the film. In the conventional anodic oxidation process, the film thickens with time. After reaching the maximum thickness, they gradually become thinner with the extension of processing time. Some alloys, such as AI-Mg and AI-Mg-Zn alloys, show this phenomenon especially. Therefore, the time of oxidation is generally controlled within the time of maximizing film thickness.

2) Properties and applications of anodic oxide film Anodic oxide film has higher hardness and wear resistance, strong adhesion capacity, strong adsorption capacity, good corrosion resistance and electrical insulation and high thermal insulation. Because of these special properties, it has been widely used in various aspects.

The main uses are: (1) improve the wear resistance, corrosion resistance, weather corrosion resistance of parts. (2) The transparent film generated by oxidation can be colored into a variety of color films. (3) as a capacitor dielectric film. (4) Improve the binding force with organic coating. For coating base. (5) for electroplating, enamel bottom. (6) Other applications being developed, such as solar absorption panels, ultra-high hardness films, dry lubrication films, catalyst films, nanowires, and deposition of magnetic alloys in porous films as memory elements.

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