Eight reasons for easy discoloration of plated coatings after colored zinc passivation in alkaline galvanizing process

Eight reasons for easy discoloration of plated coatings after colored zinc passivation in alkaline galvanizing process

Mon Jun 03 14:06:24 CST 2024

Some customers said that they used alkaline galvanized production process, after the use of colored zinc passivator, they found that the workpiece will appear very serious discoloration phenomenon, resulting in the need to return the workpiece for rework, which caused great economic losses. So, what causes the coating of the workpiece to discolor?

According to the field experience and the characteristics of the product colored zinc passivator BZ-208, Bigely Technology has made an analysis, and summarized the following eight reasons:

1. Improper addition of additives. In the production process, if the addition of additives does not adhere to the principle of frequently adding less, it is easy to cause the concentration of additives in the plating solution to fluctuate greatly. When the concentration of additives in the plating solution is higher, the greater the amount of adhesion of organic matter in the workpiece coating, so that the workpiece coating is prone to discoloration.

2. Improper ratio of zinc and alkali in the plating solution. In general, in alkaline galvanized plating solution, the ratio of alkali to zinc should be controlled at 10-15:1, when the ratio is less than 10, the stability of the plating solution is poor. If the concentration of additives is increased, although the production can be maintained, the brittleness of the galvanized layer is large, and the passivation film is easy to change color after the color passivation of the workpiece.

3, the bath temperature is high. Due to the rapid temperature rise of alkaline zinc plating solution, when the temperature of the plating solution increases, the adsorption performance of the additive decreases, the required amount and consumption will increase significantly, and the additive and organic decomposition products of the coating will also increase, so that the coating is prone to discoloration. Therefore, when the bath temperature is higher than 32 ° C, cooling measures should be used.

4, the current density is too large. When the current density is higher, the deposition rate of the coating will be faster, and the additive included in the workpiece coating will increase, and the coating is prone to discoloration after color passivation in the high current region.

5, the workpiece after galvanized washing is poor. Because the alkaline zinc bath is a strong alkaline bath and the viscosity is large, the cleaning difficulty of the workpiece after galvanizing will be relatively large. When the workpiece is not clean, it will cause the burden of the light process to increase, accelerate the failure of the light solution and the accumulation of zinc ions. Therefore, the cleaning water after galvanized should be rinsed with three countercurrent, and the cleaning water should be stirred with air, so that the effect will be better.

6, poor light solution. Because the light solution can neutralize the residual lye on the surface of the workpiece, and wash the residual organic matter on the surface of the workpiece. When the light-emitting solution is produced for a long time and is not updated in time, the accumulation of organic matter and zinc ions in the light-emitting solution leads to the failure of the light-emitting solution, and the workpiece coating is easy to change color.

7. Poor passivation. If the process parameters of the passivation liquid are not controlled properly or the colored zinc passivator with poor performance is used, the passivation liquid of the workpiece is prone to discoloration due to the unstable passivation quality of the workpiece and poor corrosion resistance. Therefore, we should choose colored zinc passivator with good corrosion resistance, such as this BZ-208, and strictly control the process parameters of the passivator.

8. Improper aging parameters. When the aging temperature of the workpiece after passivation is low or the aging time is short, the workpiece coating is also prone to poor adhesion, easy discoloration, poor corrosion resistance and other phenomena.

Therefore, the alkaline galvanizing process should pay attention to the above 8 points in the production process of using colored zinc passivator, which can effectively avoid the phenomenon of discoloration of the coating and reduce the discovery of faults. If you are interested in colored zinc passivator, please contact Bigely customer service for free samples and detailed technical information!