Electroplating on Zinc or Zinc Die-Cast

If zinc (e.g. zinc die-cast or galvanized surfaces) is already present as a substrate and an additional electroplated layer (e.g. copper, nickel, chrome, etc.) is to be applied, slightly different requirements apply than for steel. Zinc is a relatively reactive metal and can be quickly attacked by strong acids or alkalis. It also tends to form oxides, which can make good adhesion difficult. Therefore – especially with zinc die-cast – a so-called “strike” (adhesion-promoting layer) is typically used to ensure reliable adhesion for the subsequent top layer. An alkaline copper electrolyte is used as the strike layer.

Below is a recommended process sequence for electroplating on zinc or zinc die-cast:

1. Cleaning / Degreasing

   Purpose: Removal of grease, oils, and other contaminants.
   Notes: Use suitable (mild) cleaners, as zinc can be attacked in strongly alkaline media. Usually an immersion bath process, possibly supported by ultrasonic or spray cleaning.

2. Rinsing

   Purpose: Removal of cleaner residues to avoid contamination of subsequent baths.
   Tip: Multi-stage rinsing (cold or warm water) is often advisable to thoroughly clean the surface.

3. Light Pickling / Activation (Conditioner)

   Purpose: Removal of thin oxide layers and activation of the zinc surface.
   Conditioner: Special, mildly acidic bath, lightly diluted (according to manufacturer’s instructions), to gently treat the zinc surface without excessive attack.

4. Short Rinse

   Purpose: Removal of pickling or conditioner residues to avoid contaminating the following baths.

5. Strike Layer (Alkaline Copper Electrolyte)

   Purpose: Application of a very thin but strongly adhesive metal layer as a base for the subsequent coatings.
   Alkaline copper electrolyte:
   - Provides good adhesion on zinc if the surface is properly prepared.
   - Is more environmentally friendly and safer than cyanide-containing baths.

6. Main Coating

   Options:
   - Additional copper layer (acidic) for conductivity and smoothing.
   - Nickel for corrosion protection and hardness.
   - Chrome (after nickel) for gloss and wear resistance.
   - Other metals or alloys (e.g. brass, tin, bronze) as required.

7. Rinsing / Post-Treatment

   Purpose: Removal of electrolyte residues and additives.
   Optional: Passivation or sealing for additional corrosion protection or special appearance.

8. Drying / Final Inspection

   Drying: Centrifuge, warm air oven, or similar to prevent water spots.
   Final: Visual inspection, measurement of coating thickness, and adhesion tests.

Summary of Process Steps

1. Degreasing / Cleaning
2. Rinsing
3. Light Pickling / Activation (Conditioner, diluted)
4. Rinsing
5. Strike Layer (Alkaline Copper Electrolyte)
6. Main Coating (e.g. Bright Copper, Nickel)
7. Rinsing / Post-Treatment
8. Drying / Final Inspection