Electroplating encyclopedia

The low area of the galvanized layer of the workpiece turns black. Is it because the alkaline galvanizing additive is used improperly?

2022-05-13

    In the production process of using alkaline galvanizing additives, sometimes the main salt concentration of the plating solution is controlled within the normal working range, but the galvanized layer of the workpiece will appear black in the low area.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 coating in the low area of the 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?There are mainly the following 3 kinds:


    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 plating solution, the zinc coating will be dark, and blue-purple will appear after passivation, which 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 plating 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 galvanizing solution exceeds 15mg/L, the dispersing ability of the plating solution will decrease significantly, and black or gray streaks will appear on the galvanized layer after bright dipping with 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 in the low area of the workpiece coating.If you are interested in alkaline galvanizing additives, please contact Bigolly customer service to get free samples and detailed technical information!

    If you want to know more about galvanizing, you can check "Electroplating encyclopedia".