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[China Aluminum Industry Network] Analysis of the Three Causes of Uneven Color in Aluminum Oxide Film:
(1) The size of the aluminum profile workpiece is too large, and during the oxidation process, excessive oscillation occurs in the tank. This leads to uneven contact, renewal, and exchange between the edges and the center of the workpiece with the solution, resulting in inconsistent oxide film color. To prevent this issue, it's recommended to reduce the amplitude of the workpiece's movement during oxidation. In some cases, static treatment can be used instead. However, if the solution temperature is too low, a mottled or map-like appearance may occur, which looks unnatural and should be avoided.
(2) During the cladding process, some parts of the aluminum cladding may become damaged or cut off. The outer layer is usually high-quality aluminum, while the inner layer is a mix of different aluminum types. This difference in material composition can lead to irregular spots on the oxide film, resembling hurricane patterns. Many customers are unaware of this phenomenon, so manufacturers should provide clear explanations to avoid confusion and ensure customer satisfaction.
(3) Issues during the oxidation process:
1. Incomplete alkali etching, leaving original oxide layers or dirt on the surface.
2. Failure to perform light treatment immediately after alkali etching, causing the workpiece surface to remain alkaline.
3. Contact with foreign materials during the transfer of the workpiece.
When uneven colors appear on the oxide film, it's essential to investigate multiple factors and implement targeted solutions.
One reader asked why it was difficult to form a conductive oxide film after alkali etching. After eliminating other possible causes, we considered whether the alkali solution had accumulated too many aluminum ions. The reader mentioned that the solution was very thick but not very corrosive. Based on experience, we suggested replacing the solution, as prolonged use leads to excessive aluminum ion buildup, which hinders the formation of a conductive oxide layer by preventing proper contact between the workpiece and the solution. Another recommendation was to rinse the workpiece in hot water immediately after alkali etching, then treat it with concentrated nitric acid containing hydrofluoric acid, followed by thorough rinsing before oxidation. After following this advice, the reader reported significantly improved results. From our experience, it’s important to quickly move the workpiece from hot water to running water to prevent oxidation and ensure effective conductive oxide film formation.
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Zhoushan Jinsheng Bimetallic Plastic Machinery Factory , https://www.jinshenggalloy.com