Reasons for Yellowing of Cold Galvanizing

Why does the galvanized layer turn yellow after using blue and white zinc passivation solution

 

Author: Marisa

Why does the galvanized layer turn yellow after using blue and white zinc passivation solution?

1. Improper ratio of passivation solution: The concentration of certain components in the passivation solution is too high or too low, especially the concentration of chromate or divalent chromium in the passivation solution, which may cause yellowing on the surface of the galvanized layer.

2. Improper passivation time: If the passivation time is too long, a thick chromium film will form on the surface of the galvanized layer, which is prone to yellowing due to oxidation and other reasons.

 

3. Excessive drying temperature: If the drying temperature of the plated part after passivation is too high, it can also cause the surface of the coating to turn yellow, as excessive temperature may accelerate the oxidation process of the coating surface.

4. Storage environment issue: If the storage environment has high humidity, the surface of the galvanized layer may turn yellow due to absorption of these gases or moisture.

 

5. Insufficient cleaning: Insufficient cleaning before galvanizing can cause residual impurities or dirt to have adverse reactions during passivation, resulting in localized or overall yellowing.

 

6. Plating solution pollution: During the galvanizing process, if the plating solution contains pollutants such as high iron ion concentration, it can also cause color changes in the coating after passivation.

 

7. Environmental oxidation: When exposed to oxidizing environments such as oxygen and moisture in the air, the surface of the coating may undergo oxidation reactions, resulting in a yellowing of the color.

 

8. Physical damage: The coating may suffer from physical damage such as friction during processing, handling, or storage, which may damage the passivation film and allow moisture or oxygen to easily penetrate into the interior of the coating, causing yellowing.

 

To accurately determine the cause of yellowing of zinc plating, it is usually necessary to conduct a comprehensive analysis based on specific information such as production process flow, environmental conditions, and replacement of blue and white zinc passivation solution. The solution to the yellowing problem usually includes adjusting passivation process parameters, improving post-treatment and drying methods, optimizing storage conditions, and other measures.