Acid Zinc Plating Process Skills

The acid zinc plating process is widely used for corrosion protection and decorative finishes on metal parts.

 

Author: Marisa

The acid zinc plating process is widely used for corrosion protection and decorative finishes on metal parts.

Here are key skills and best practices to ensure high-quality plating:

1. Pre-Treatment (Critical for Adhesion & Quality)

• Cleaning: Remove oils, grease, and dirt using alkaline degreasing or ultrasonic cleaning.

• Acid Pickling: Use HCl or H₂SO₄ to remove rust and oxides.

• Activation: A mild acid dip (e.g., 5-10% HCl) ensures a clean, active surface.

2. Bath Composition & Control

• Zinc Chloride (ZnCl₂): 60–120 g/L (primary zinc source).

• Potassium Chloride (KCl): 180–250 g/L (conductivity enhancer).

• Boric Acid (H₃BO₃): 25–30 g/L (pH buffer, stabilizes bath).

• Brighteners: Organic additives (carriers, brighteners, levelers) for smooth, shiny deposits.

• pH Control: Maintain 4.5–6.0 (adjust with HCl or KOH).

3. Operating Conditions

• Temperature: 20–35°C (higher temps increase plating speed but reduce brightness).

• Current Density: 1–5 A/dm² (adjust for part geometry).

• Agitation: Mild air or mechanical agitation ensures uniformity.

• Filtration: Continuous filtration (5–10 µm) prevents defects.

4. Common Issues & Troubleshooting

• Dull Deposits:

  • Check brightener levels (too low or exhausted).

  • Verify pH and temperature.

• Poor Adhesion:

  • Ensure proper pre-treatment (cleaning & activation).

  • Check for contamination (metallic impurities like Cu, Pb).

• Burning at High Current Density:

  • Reduce current density or improve agitation.

• White Stains/Blotches:

  • Rinse thoroughly after plating.

  • Check for chloride/zinc imbalance.

5. Post-Treatment

• Passivation (Chromate/Trivalent Conversion):

  • Yellow, blue, or black chromate for corrosion resistance.

  • RoHS-compliant trivalent passivates (e.g., Cr³⁺).

• Drying: Hot air drying to prevent water spots.

• Sealing (Optional): Silicate or lacquer topcoat for enhanced durability.

6. Maintenance & Waste Control

• Regular Analysis: Monitor Zn²⁺, KCl, boric acid, and additives via Hull cell tests.

• Purification: Use dummy plating or zinc dust to remove metallic impurities.

• Waste Treatment: Neutralize acidic waste before disposal (Ca(OH)₂ precipitation).

Pro Tips

• Rack Design: Ensure proper current distribution for complex parts.

• Anode-to-Cathode Ratio: ~1:1 (use titanium baskets with pure zinc balls).

• Avoid Over-Plating: Excess thickness reduces brightness and increases brittleness.

By mastering these skills, you can achieve consistent, high-quality acid zinc plating with excellent corrosion resistance and appearance. Let me know if you need details on a specific aspect!