Zinc plating product surface fogging (also called blushing or hazing) refers to a cloudy, milky, or dull appearance on the plated surface, often caused by improper plating conditions or post-treatment processes. Below are the common causes and treatment methods:
Author: Robby
Zinc plating product surface fogging (also called blushing or hazing) refers to a cloudy, milky, or dull appearance on the plated surface, often caused by improper plating conditions or post-treatment processes. Below are the common causes and treatment methods:
Poor Rinsing After Plating
Residual plating solution or chemicals left on the surface can cause fogging.
Inadequate rinsing after acid activation or cyanide zinc plating leads to chemical residues.
Improper Passivation
Chromate passivation film not properly formed due to:
Incorrect pH or temperature.
Contaminated passivation solution.
Insufficient or excessive immersion time.
Hydrogen Embrittlement & Absorption
Hydrogen bubbles trapped on the surface during plating can cause fogging.
Common in high-current-density areas or when brighteners/dehydrogenation are insufficient.
Contaminated Bath or Additives
Organic brightener breakdown products or metallic impurities (Fe, Cu, Pb) in the zinc bath.
Excessive carbonates in alkaline zinc baths.
Drying Issues
Slow or improper drying allows water stains or oxidation before complete drying.
High humidity in the storage environment can cause moisture absorption.
Poor Base Metal Preparation
Oils, oxides, or rust on the substrate before plating lead to uneven zinc deposition.
Use overflow rinsing or counter-current rinsing to ensure thorough cleaning.
Introduce hot DI water rinsing (50–70°C) to reduce water marks.
Control passivation bath parameters (pH, temperature, immersion time).
Use fresh passivation solution and avoid contamination.
Apply drying aids (e.g., hot air blow-off) immediately after passivation.
Perform post-plating baking (200–220°C for 2–4 hours) for high-strength steels.
Optimize current density and use hydrogen-reducing brighteners.
Regularly filter and purify the zinc plating bath.
Use carbon treatment to remove organic contaminants.
Monitor and control carbonate levels (use cooling or chemical removal methods).
Use forced hot air drying (80–100°C) immediately after rinsing.
Apply anti-fogging agents or water-displacing lubricants before drying.
Ensure proper degreasing, acid pickling, and activation before plating.
Use electrolytic cleaning for critical parts.
Light fogging: Remove with a dilute acid dip (1–5% HNO₃ or citric acid) + re-passivation.
Severe fogging: Strip and re-plate after identifying the root cause.
| Cause | Solution |
|---|---|
| Poor rinsing | Improve rinsing, use DI water, hot rinsing |
| Passivation issues | Adjust pH/temperature, replace bath |
| Hydrogen embrittlement | Bake parts, optimize current density |
| Bath contamination | Carbon treatment, filtration |
| Drying problems | Hot air drying, anti-fog agents |
| Poor pre-treatment | Enhance cleaning & activation |
By addressing these factors, zinc plating fogging can be minimized, ensuring a bright, uniform, and corrosion-resistant finish.