During the application of acid zinc plating brightener, the post-zincation passivation mainly includes blue-white passivation and rainbow color passivation. However, in some cases, the rainbow color passivation may have problems such as poor adhesion between the film layer and the substrate and easy peeling. What's the reason for this?
1. The current density during galvanizing is too high. During the production process, sometimes to increase production efficiency and shorten the electroplating time, the current is increased. Some people even add cathode movement. Although this increases the deposition speed, it is prone to cause excessive organic impurities in the coating layer, resulting in a brittle coating. After color passivation, the passivation film is likely to fog, lose luster, and have poor adhesion. Therefore, it is best not to increase the current or add cathode movement.
2. There is excessive impurity of organic substances in the galvanized layer. Some manufacturers, in an attempt to enhance the brightness of the galvanized layer, frequently add acid galvanizing brighteners. This results in an excessively high content of the brightening agent in the solution. Moreover, some of these brightening agents have high content of surfactants on their surface, making it very likely for organic substances to be mixed into the coating during production. At this point, the adhesion of the passivation film will be poor, and it is prone to peeling and fading.
3. Inadequate water washing. Acid galvanizing imposes stringent requirements on post-plating processing, particularly water washing. Organic films adsorbed on the workpiece surface must be thoroughly removed to ensure good adhesion of the passivation film.
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