Factors affecting the oxidation coloration of aluminum alloy
At present, the application of single-color anodized aluminum alloy building profiles in practice has been significantly reduced, and based on it, electrolytic colored oxide film, organic colored oxide film and porcelain oxide film, hard oxide film, imitation stainless steel oxide film Etc. has been widely used. For the oxidation film coloring technology, the factors affecting the oxidation coloration of aluminum alloy are:
1. Influence of impurities in electrolytic solution
The degree of coloration of aluminum alloy products depends largely on the quality of the formation of the oxide film. Therefore, in the anodizing solution of sulfuric acid, the influence of impurities on the oxide film can not be ignored. The impurities are mainly metal ions such as copper, iron, aluminum and organic impurity pollutants, which should be removed in time to maintain the normal use range of the solution.
(1) The copper ions are displaced and deposited on the surface of the aluminum member, causing the oxide film to loosen and lowering the transparency, corrosion resistance and electrical insulation properties. Therefore, the copper ion content is not allowed to exceed 0.02 g/L.
(2) The chloride ion is from the tap water or the cooling water after the cooling tube is broken. The chloride ion content should be less than 0.2g/L. Otherwise, the oxide film formed is rough and loose, and the surface of the aluminum part is etched (breakdown).
(3) The aluminum ion in the aluminum ion electrolyte is gradually increased. When the content is more than 25g/L, the conductivity of the electrolyte decreases, white spots or blocky white spots appear on the surface of the workpiece, and the adsorption capacity of the film decreases, and the dyeing is difficult. .
(4) Iron ions in the iron ion electrolyte are not allowed to exceed 0.2 g/L, otherwise dark streaks may appear.
(5) Organic impurities hinder the formation of an oxide film, and after the film adsorbs oil stains, the coloration is uneven and streaks appear.
2. Factors affecting the color quality of oxide film
(1) If the pre-treatment degreasing process is not thorough, it will cause obvious white spots on the film layer, which will cause difficulty in coloring.
(2) When the concentration of Sn salt in the electrolytic solution is too low, the coloring speed is slow. When the concentration is higher than 25g/L, the coloring speed is fast, but it is difficult to grasp, and the color difference is often large. .
(3) The coloring temperature has a great influence on the coloring. When the temperature is lower than 15 ° C, the coloring speed is slow. When the temperature is too high, the colored film is fogged, and the Sn salt is easily hydrolyzed, thereby causing the bath to be turbid.
(4) Time: The length of the coloring time will also affect the coloring quality and color fastness, such as short coloring time, light color and easy to fade, long time, too dark color, and the surface is easy to bloom.
(5) When the coloring voltage is low, the coloring speed is slow, the color change is slow, and uneven color tone is likely to occur. When the voltage is high, the coloring speed is fast, and the colored film is easily peeled off.
(6) In the case of anodizing film formation or electrolytic coloring, a surfactant-based additive and a stabilizer are added, the purpose of which is to stabilize the film formation rate and film thickness, suppress the dissolution of the oxide film, and improve the coloring. Uniformity.
In addition, the pH value, water quality, and coloring tank materials all have certain influence on the coloring quality, and the quality of the electrolytically colored oxide film can be ensured only by ensuring that each parameter is within the control range.