technical description of oxidation treatment:
1. chemical oxidation
the coating obtained by chemical oxidation treatment is relatively thin, with a thickness of 0.5μm ~ 4μm. it is soft and not wear-resistant, and its corrosion resistance is lower than that of anodic oxidation film. generally should not be used alone, because the chemical oxide film adsorption capacity is good, mainly on the bottom of the paint, chemical oxidation according to its solution can be divided into alkaline and acidic two. according to the film properties can be divided into oxide film, phosphate film, chromate film and phosphate monochromate film, etc. (this type of oxide film is conductive)
2. electrochemical oxidation
electrochemical oxidation (commonly known as anodic oxidation) is aluminum and aluminum alloy in the corresponding electrolyte and specific process conditions, due to the action of impressed current. the formation of an oxide film on aluminum and its alloys is called anodic oxidation (this oxide film is not conductive)
3. hard anodic oxidation
hard generating mechanism of the oxidation film, the same as the ordinary sulfuric acid anodic oxidation, but in order to get thick and hard film, need to adopt 0 centigrade degrees of electrolyte, and the method of high voltage and high current, make the formation rate greater than the dissolution rate of membrane, the membrane layer structure changes, constitutes the new characteristics of hard oxidation film growth process. hard oxide film is also a double layer structure, the difference is that the thickness of the barrier layer is 10 times larger than that of the ordinary oxide film, so is the hole wall, which is one of the basic reasons for high hardness. however, the porosity is 7 ~ 8 times less than that of ordinary oxide film. only 2% ~ 6%, the hard film base group chaotic interference with each other, a special prism. lead to high stress in the film, and even cause cracking, residual alloy elements and electrolytic decomposition products in the film wall. the color of oxide film is dark and the color of alloy composition is different. alloy composition and impurities, hard oxidation has a greater impact, it affects the uniformity and integrity of oxide film, aluminum copper, aluminum silicon. aluminum alloy, hard oxidation is more difficult.
4. structure of aluminum anodic oxide film.
the oxide film is composed of a barrier layer and a porous layer. the porous layer is composed of a number of oxide groups with hexagonal columns (membrane cells), each of which has a hexagonal hole in the center. shaped like a honeycomb, the thickness of the pore wall is twice the diameter of the pore. the average porosity of sulfuric acid anodic oxidation film is 20% ~ 30%, and there are about 800 holes on the surface of 1μm2, so the anodic oxidation can be a variety of colors.
5. coloring of anodic oxide film
anodized films are porous, chemically active and easy to stain. aluminum oxide film has 20% ~ 30% pores (sulfuric acid film), so there is a huge specific surface area of chemical activity, dye molecules through the oxide film physical and chemical adsorption accumulated in the inner surface and color. the porosity of hard oxide film is less than ordinary oxide film, the hole is deep, the diameter is small, the coloring is difficult than ordinary oxide film, and the hard oxide film is thick film, because of the different alloy. it has a darker background, so black is ideal.
6. sealing treatment after anodic oxidation
aluminum anodic oxide film has a high porosity, and adsorption capacity, easy to be polluted and corroded, medium erosion, therefore, no matter whether the oxide film is colored or not, used for what occasions, must be closed treatment, the purpose is to improve the corrosion resistance. improve the anti-pollution ability and fixed pigment, such as special follow-up treatment can not be closed, increase the adsorption capacity.