Method for cleaning blind holes of aluminum alloy parts after chromic acid anodization

Chromic acid anodic oxidation is one of the surface treatment methods to enhance the corrosion resistance of aluminum alloy parts. The aluminum alloy parts are used as anodes, placed in a chromic acid solution of a specified concentration, and energized within a certain temperature range. A layer of oxide film with good elasticity, grayish white to dark gray and opaque is formed on the surface, and the thickness is 05-15μm. The acid oxide film has almost no holes, so the film layer can be used normally without sealing treatment. The process of chromic acid anodization: installation → chemical degreasing → hot water washing and cold water washing → alkali corrosion-hot water washing-cold water washing →Light out→flowing cold water washing→chromic acid anodizing→flowing cold water washing→drying→drying→inspection.

The chromic acid anodizing solution contains chromic anhydride (CnO) 30-40g/L, and the anodizing working temperature is 38-42℃.

Chromic acid anodic oxidation of aluminum alloy parts is carried out in industrial batch production using hangers and cranes. But for the parts with blind holes, especially the parts with small size blind holes, the chromic anhydride solution entering the blind holes during the anodizing process is not easy to clean because of the large number of parts processed in each tank. The parts with blind holes are cleaned visually, and after blowing and drying, the surface of the parts shows a uniform and smooth chromic acid anodized film. Placed for several days, especially when the storage environment is relatively humid, there will be brown-red chromic anhydride flow marks in the blind holes, which will contaminate the film on the surface of the part, which will affect the appearance quality of the part. It will corrode the surface of parts and blind holes. The main reason for this phenomenon is that the chromic acid solution remaining in the blind holes is difficult to clean. In addition, chromic anhydride has strong acidity and strong corrosiveness and dyeing ability after being dissolved in water. Even a small amount of residue will cause parts The appearance is brownish red. After being placed for a long time, it is corroded, the bottom diameter of the blind hole becomes larger, and the surface of the part after wiping becomes white. Therefore, how to clean the parts after anodizing is the key to solving this problem.