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The low-area coating of the alkali zinc workpiece is blackened, which is not due to improper use of alkali zinc plating additives

2022-05-27

    In the production process of alkaline zinc plating, sometimes the main salt concentration of the alkaline zinc plating solution is controlled within the normal working range, but the galvanized layer in the low area of the workpiece will turn black,Is this an improper use of alkaline galvanizing additives?

    Bigolly Technology made an analysis based on the field experience and the characteristics of the product's alkaline galvanizing additives BZ-515,In fact, the blackening of the low area of the galvanized workpiece is not caused by improper use of alkaline galvanizing additives, but because the content of metal impurities in the plating solution is too high.What metal impurities can cause blackening of the low area of the galvanized layer?


    1. Iron impurities.Iron impurities are mainly brought in by inferior sodium hydroxide or workpieces.When the iron ion content in the alkaline zinc plating solution exceeds 50mg/L, colloidal flocs will appear in the alkaline zinc plating solution, the zinc coating will be dark, blue-purple will appear after passivation, and it is easy to foam.

    2. Copper impurities.Copper impurities are mainly brought in by hooks and when washing copper rods.When the copper ion content in the alkaline zinc solution reaches 20 mg/L, the coating is rough and dark, and the brightness decreases significantly, and the bright area of the coating is also reduced.

    3. Lead impurities.Lead impurities are mainly brought in by inferior zinc anode plates.When the lead ion impurity in the alkaline zinc plating solution exceeds 15mg/L, the dispersing ability of the plating solution will be significantly reduced, and black or gray streaks will appear on the zinc coating after dilute nitric acid.

    Therefore, in the production process of using alkaline galvanizing additives, we should strictly control the metal impurities in the plating solution, and regularly treat the plating solution with zinc powder to avoid the phenomenon of blackening of the coating in the low area of the workpiece.If you are interested in alkaline galvanizing additives, please contact Bigolly customer service to get free samples and detailed technical information!

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