Why does the color of the aluminum oxide film appear uneven?

Three possible reasons for the uneven color of the aluminum oxide film: The main results are as follows: (1) The workpiece area is too large, the swing in the tank is too large, the edge of the solution is in contact with the center, renewal and exchange are too large, resulting in inconsistent color of the oxide film. Prevention method: during the oxidation process, the swing of the workpiece is small, and static treatment can also be used. However, when the temperature of the solution is too low, map-like spots are prone to appear, which is unnatural. (2) The aluminum coating is partially destroyed and cut off during the processing. The outer layer of aluminum is high-quality aluminum, and the inner layer is mixed aluminum. There is a big difference between the two types of aluminum. Vitiligo spots appear after oxidation. Customers often don't understand this phenomenon. , The manufacturer should do more explanation work, explain the original work, so as not to cause misunderstanding. (3) Process operation problems (1) The alkali corrosion treatment of the workpiece is not thorough, and the original oxide film and dirt cannot be partially removed; (2) The surface of the workpiece is still alkaline when the light treatment is not performed immediately after the alkali corrosion. (3) The workpiece has been in contact with foreign objects during the transfer process. When the color of the film layer is not uniform, we should find out the cause from multiple aspects and take targeted measures to solve it. Due to the excessive accumulation of aluminum ions in the alkaline corrosion solution, a reader called to ask why it is difficult to obtain a conductive oxide film after alkaline corrosion. After eliminating many factors that make it difficult to form conductive oxide films, considering that the content of aluminum ions in the alkaline etching solution is too high, the other side thinks that the alkaline etching solution is very thick. But the alkali corrosion rate is not fast. At that time, the author suggested to replace the alkaline etching solution, because after the alkaline etching solution is used for too long, aluminum ions will accumulate too much and it is difficult for aluminum ions to be eluted on the surface of the workpiece, which affects the contact between the surface of aluminum parts and the conductive oxide solution, thereby affecting the oxide film Formation. Another suggestion is that if the alkaline etching solution is replaced unconditionally at that time, the alkaline etching workpiece can be rinsed in running water immediately after washing with hot water, and then brightened in concentrated nitric acid containing hydrofluoric acid, and then conduct conductive oxidation after sufficient washing. . After that, readers called and said that washing and ironing with hot water worked well after alkaline erosion. The author’s experience is that after washing and ironing in hot water, the hot water will quickly leave and be immersed in tap water immediately to prevent the formation of conductive oxide film caused by the oxidation of the workpiece after drying.
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