In addition to the metal coating layer, a dense compound film (transformation film) can also be formed on the surface of copper products through chemical or electrochemical methods, or a colored film layer can be generated. This not only enhances the corrosion resistance but also serves as a decorative function.
1. Passivation treatment: Prevent oxidation discoloration
The main purpose is to enhance the corrosion resistance of copper and prevent oxidation discoloration during transportation and storage. The commonly used passivating agents are some organic compounds, which can form a protective film with copper. Previously, chromate solutions were commonly used, but due to environmental concerns, they have gradually been replaced.
2. Chemical coloring: Achieve colored appearance
By controlling the reaction between copper and specific chemical solutions (such as potassium sulfide, ammonia water-related solutions), a colored film layer is formed on the surface. Common colors include bronze, bronze, blue, green, black, etc. It is commonly used in handicrafts, building hardware, and decorative items. The process is: pre-treatment (oil removal, etching) → coloring → water washing → drying → applying transparent protective paint (fixing color, extending service life).
3. Anodic oxidation: Form a thin oxide film
Unlike aluminum, copper cannot form a thick oxide film through anodic oxidation. However, when subjected to anodic treatment in a specific electrolyte, a thin and dense oxide film can be formed. It is commonly used in capacitor manufacturing or as a base for coloring.
※ Summary
The coating and surface treatment technologies for copper and copper alloys form a complex system, involving multiple processes. From pre-treatment as a foundation, to electroplating, chemical plating to achieve functionality and decoration, to hot-dip plating for thick protection, and to conversion films and coloring treatments to enhance durability and aesthetics, each technology has its own application scenarios and process requirements.
In actual production, the appropriate surface treatment technology should be selected based on the material of the copper product, the usage environment, performance requirements, and cost budget. Quality control must also be done well to produce high-quality products. With increasingly strict environmental requirements, in the future, more non-cyanide electroplating, low-toxic and harmless chemicals, energy-saving equipment, and intelligent control technologies will be adopted.