Color passivation (typically using hexavalent or trivalent chromate) is a post-treatment for zinc, cadmium, and aluminum coatings. It enhances corrosion resistance, appearance, and functionality.
Author: Anna
Color passivation (typically using hexavalent or trivalent chromate) is a post-treatment for zinc, cadmium, and aluminum coatings. It enhances corrosion resistance, appearance, and functionality. Below are the key advantages:
Forms a protective chromate layer that acts as a barrier against moisture, salt, and chemicals.
Can extend the lifespan of zinc-plated parts by 5–10 times compared to untreated surfaces.
Hexavalent chromate (Cr⁶⁺) offers the best protection but is being phased out due to toxicity.
Trivalent chromate (Cr³⁺) is an eco-friendly alternative with good performance.
Provides uniform, colorful coatings (e.g., blue, yellow, olive, black) for visual appeal.
Used in consumer electronics, automotive trims, and decorative hardware.
The slightly porous chromate layer helps paint, powder coatings, and adhesives bond better.
Prevents peeling, blistering, or flaking of topcoats.
If scratched, hexavalent chromate can "self-repair" by migrating to damaged areas, maintaining protection.
Trivalent chromate lacks this feature but still provides strong passive protection.
Unlike phosphating, chromate coatings do not significantly interfere with electrical contacts.
Used in connectors, terminals, and EMI shielding.
The coating is extremely thin (0.5–2 microns) but highly effective, avoiding dimensional changes.
Ideal for precision components like fasteners and small mechanical parts.
Resists fuels, oils, and mild acids, making it suitable for automotive and aerospace applications.
| Feature | Hexavalent (Cr⁶⁺) | Trivalent (Cr³⁺, RoHS-Compliant) |
|---|---|---|
| Corrosion Resistance | Excellent (self-healing) | Good (but no self-repair) |
| Appearance | Iridescent yellow, olive, black | Usually blue, clear, or black |
| Environmental Impact | Toxic (restricted by RoHS/REACH) | Eco-friendly, widely used |
| Cost | Lower (but declining use) | Slightly higher |
✔ Automotive: Zinc-plated bolts, brake components, fuel system parts.
✔ Electronics: Connectors, shielding cans, antenna parts.
✔ Aerospace: Cadmium-plated fasteners (with chromate for corrosion resistance).
✔ Consumer Goods: Door handles, light fixtures, bathroom hardware.
✅ Best for corrosion protection – Especially in harsh environments.
✅ Decorative and functional – Available in multiple colors.
✅ Thin yet durable – Does not affect part dimensions.
✅ Hexavalent chromate is being replaced by trivalent due to environmental regulations.
Color passivation remains a critical finishing process for zinc and cadmium coatings, balancing performance, aesthetics, and compliance with modern environmental standards.