Factors Affecting Oxidation Coloring of Aluminum Alloys

【ALUMINIUM NETWORK】At present, the application of single-color anodized aluminum alloy building profiles has been significantly reduced in practice, and electrolytic coloring oxide films, organic colored oxide films, and porcelain oxide films, hard oxidation based on them have been significantly reduced. Films, imitation stainless steel oxide films, etc. have been widely used. For the oxide film coloring technology, the factors affecting the oxidation color of aluminum alloys are:

1. Influence of Impurities in Electrolytic Solution The degree of coloration of aluminum alloy products depends on the quality of the oxide film. Therefore, in the anodizing solution of sulfuric acid, the impact of impurities on the oxide film can not be ignored, the impurities are mainly copper, iron, aluminum and other metal ions and organic impurities, should be promptly removed to maintain the normal use of the solution.

(1) Copper ions will be deposited on the surface of aluminum parts, resulting in loose pores in the oxide film, and reduce the transparency, corrosion resistance, and electrical insulation properties. Therefore, the copper ion content must not exceed 0.02 g/L.

(2) Chloride ions come from tap water or cooling water after cooling pipe rupture. Chloride ion content should be less than 0.2g/L. Otherwise, the resulting oxide film is rough and loose. In severe cases, the surface of the aluminum part is eroded (breakdown).

(3) The aluminum ion in the aluminum ion electrolyte gradually increases. When the content is more than 25 g/L, the conductivity of the electrolyte decreases, the surface of the product shows white spots or blocky white spots, and the adsorption capacity of the film layer decreases, and the dyeing is difficult. .

(4) Iron ions in ferric electrolytes are not allowed to exceed 0.2 g/L, otherwise dark streaks will appear.

(5) Organic impurities will hinder the formation of oxide film. After the film absorbs oil stains, the coloration will be uneven and flower spots will appear.

2. Factors affecting the coloring quality of the oxide film (1) If the degreasing process of the pre-treatment is incomplete, it will cause obvious white spotting on the film layer, which will cause difficulty in coloring.

(2) When the Sn salt concentration in the electrolytic solution is too low, the coloring speed is slow, and when the concentration is higher than 25 g/L, the coloring speed is fast, but it is not easy to grasp, and there is often a large color difference. .

(3) The coloring temperature has a great influence on the coloring. When the temperature is lower than 15°C, the coloring speed is slow. If the coloring temperature is too high, the coloring film will be fogged, and the Sn salt will be easily hydrolyzed and cause the turbidity of the bath.

(4) Time: The coloring time will also affect the coloring quality and color fastness. For example, the coloring time is short, the color is light and easy to fade, the time is long, the color is too dark, and the surface is prone to flowering.

(5) When the coloring voltage is low, the coloring speed is slow, the color change is slow, and the color tone unevenness is easy to occur. When the voltage is high, the coloring speed is high and the coloring film is easily peeled off.

(6) Additives and stabilizers mainly composed of surfactants are added in the filming of anodic oxidation or electrolytic coloring. The purpose is to stabilize the film-forming speed and film thickness, inhibit the dissolution of the oxide film and improve the coloring. Uniformity.

In addition, the pH value, water quality, and coloring tank material all have a certain influence on the coloring quality. Only by ensuring that each parameter is within the control range can the quality of electrolytic coloring oxide film be guaranteed.

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