The influence of the structure of azo compounds on the deposition process and the quality of copper coatings on Anodized aluminum alloys

A comparative analysis of the influence of the structure of azo compounds (on the example of methyl red (MKR) and nitroso-p-salt (NRS)) was carried out during copper plating of anodized aluminum alloys, on the microstructure, micro-roughness and quality of deposited copper coatings. It is shown that the choice of azo dye significantly depends on the charge of the surface of the oxide film in the solutions used. It is shown that the dyes used should have at least two functional groups in their composition, one of which should ensure the formation of complexes with copper ions, and the other – their adhesion to the surface of the oxide film due to the forces of electrostatic interaction. The adsorption of azo compounds changes the structure of the double electric layer at the film – electrolyte interface, which affects the speed of the copper plating process. At the same time, the mobility of the formed complexes in the adsorption layer increases, which leads to a better opening of the film surface. The studied indicators (dyes) positively affected the structure of the copper coating (eliminated defects and made it fine-crystalline), and also significantly smoothed the surface of the copper coating. The advantage of using the NRS over the MKR was revealed, which allowed not only to obtain a high-quality coating, but also to significantly intensify the copper plating process. A new composition of copper sulfuric acid electrolyte for coating anodized aluminum alloys at elevated cathode current densities with preservation of fine-crystalline structure and smoothed surface is proposed.