Causes And Solutions for The Appearance of Black Spots on 7075 Aluminum Alloy After Anodizing

The causes for the appearance of black spots on 7075 aluminum alloy after anodizing mainly include chemical reactions, improper treatment conditions, unclean raw materials, electrolyte contamination, and uneven heat treatment, etc. The solutions to these problems involve adjusting the parameters of the anodizing treatment, ensuring the cleanliness of raw materials, controlling the purity of the electrolyte, and improving through repeated heat treatment processes.

Chemical Reactions: During the anodizing process, an electrochemical reaction occurs on the surface of the aluminum alloy, forming an oxide film. During the formation of this oxide film, some black spots may be formed. Especially in the case of 7075 aluminum alloy, due to its relatively high zinc content in its composition, this situation is more likely to occur.

Improper Treatment Conditions: Factors such as the oxidation time, current density, and the concentration of the electrolyte solution in the anodizing treatment can all affect the quality and appearance of the oxide film. If these conditions are not properly controlled, black spots may appear on the surface of the oxide film.

Unclean Raw Materials: There may be some impurities or contaminants on the surface of the aluminum alloy, such as grease, fingerprints, dust, etc. These impurities may be oxidized into black spots during the anodizing process.

Electrolyte Contamination: During the anodizing process, impurities or contaminants in the electrolyte solution may also form black spots on the surface of the oxide film.

Uneven Heat Treatment: The reason for the black spot defects on the surface of 7075 aluminum alloy parts is that there are more undissolved particle phases in the microstructure. The internal and external causes are respectively the segregation of Zn, Cu, and Mg elements inside the material and the uneven heat treatment of the parts themselves. Appropriate repeated heat treatment processes can eliminate the black spot defects on the surface of the parts.

To address the problem of black spots appearing on 7075 aluminum alloy after anodizing, the following solutions can be adopted:

Optimize the Anodizing Treatment Process: Adjust parameters such as the oxidation time, current density, and the concentration of the electrolyte solution to ensure that they are within a reasonable range, so as to improve the quality and appearance of the oxide film.

Strengthen the Cleaning of Raw Materials: Before the anodizing treatment, thoroughly clean the surface of the aluminum alloy to remove impurities such as grease, fingerprints, and dust on the surface, ensuring that the surface is clean and free of contaminants.

Use High-Purity Electrolyte: Select a high-purity electrolyte solution and avoid using solutions containing impurities or contaminants to reduce the black spots on the surface of the oxide film.

Pickling Treatment: If black spots have already appeared after anodizing, you can try to use a pickling agent to perform pickling treatment on the surface of the aluminum alloy. Pickling can remove the oxide layer and spots on the surface, providing a clean surface for recoating or further processing.

Electrolytic Polishing or Chemical Polishing: After pickling, electrolytic polishing or chemical polishing techniques can be used to polish the surface of the aluminum alloy to improve its smoothness and brightness and remove tiny defects and contaminants on the surface.

Coating Protection: Finally, use coatings suitable for 7075 aluminum alloy to perform recoating treatment to protect its surface and prevent the appearance of oxidation spots in the future.

It should be noted that before dealing with the problem of black spots, the causes should be carefully examined and analyzed so as to better select targeted solutions. Meanwhile, in daily use, attention should also be paid to keeping the usage environment of aluminum alloy products dry and clean to avoid the appearance of oxidation spots on the surface due to environmental factors.

Through the above methods, the problem of black spots appearing on 7075 aluminum alloy after anodizing can be effectively solved, and the quality and appearance of the products can be improved.