[China Aluminum Industry Network] In recent years, in the surface treatment technology of aluminum, aluminum-plastic board and honeycomb board, there is a trend toward the development of anodizing technology. For the anodizing treatment of aluminum plates, aluminum-plastic plates and honeycomb plates, the uniformity of the thickness of the anodized film, the uniformity and reproducibility of color should be noted. To ensure the uniformity of the thickness of the anodized film, the uniformity and reproducibility of the color, it is necessary to strictly control the chemical composition of the aluminum alloy and the production process of the anodization.
1, strictly control the casting production process. The chemical composition of the ingot must be controlled as small as possible and the chemical composition must be uniform. In addition, the smelting process, casting process and homogenization process must be strictly implemented.
2, choose the right fixture. The mounting fixture material must ensure good electrical conductivity. Copper or copper alloy fixtures are generally used. Used special or general-purpose fixtures, such as those re-used during anodization, must have their surface oxide film removed to ensure good contact.
3, strictly control the anodizing temperature. From the mechanism of anodic oxidation film formation, it can be seen that when the anodic oxidation temperature is low, the formed oxide film is dense and the porosity is small. As the anodic oxidation temperature increases, the oxide film gradually loosens, the porosity gradually becomes larger, and the color of the film layer becomes larger. Gradually darkens with increasing temperature. Therefore, the anodizing temperature is an important factor in determining the degree of densification of the oxide film, and is also an important factor in determining the color uniformity of the oxide film.
4. Strictly control the anodizing current density. With the increase of the current density, the color of the oxide film gradually darkens, and the thickness of the film first becomes thicker and then becomes thinner. The reason is that the current density increases, the pores of the film increase, and it is easy to be colored; the current density decreases, and the film thickness decreases. The growth rate decreases and the film is dense. As the current density increases, the color of the oxide film gradually darkens. Under the other conditions unchanged, the current density is increased, the growth rate of the oxide film is accelerated, the oxidation time can be shortened, the amount of chemical dissolution of the film is reduced, the film is hard, and the wear resistance is good. However, the current density cannot be raised too high. Otherwise, due to Joule heating, the thermal effect in the film hole increases, the local temperature rises significantly, the dissolution rate of the oxide film increases, and the film formation rate decreases. In other words, when the current density is increased, the film formation rate can be increased within a certain range, but after a certain value is reached, the film formation rate is decreased. The size of the current density directly affects the uniformity of the color of the oxide film.
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