What colors are available for the zinc electroplating passivation process

In the zinc electroplating passivation process, the color of the coating is determined by the type of passivation treatment applied after plating. Different passivation chemistries produce various colors, each offering unique corrosion resistance and aesthetic properties. Here are the most common colors available:

Author: Robby

In the zinc electroplating passivation process, the color of the coating is determined by the type of passivation treatment applied after plating. Different passivation chemistries produce various colors, each offering unique corrosion resistance and aesthetic properties. Here are the most common colors available:

1. Clear / Blue-Bright Passivation

• Appearance: Shiny, silvery-blue or clear finish.

• Properties:

  • Basic corrosion resistance (typically 24–72 hours to white rust in salt spray tests).

  • Maintains the natural metallic look of zinc.

• Common Uses: Fasteners, decorative parts, electronics.

2. Yellow (Iridescent) Passivation

• Appearance: Golden-yellow or iridescent hue.

• Properties:

  • Better corrosion resistance than clear passivation (72–96+ hours salt spray).

  • Contains hexavalent chromium (Cr⁶⁺) in traditional processes, but many now use trivalent chromium (Cr³⁺) for environmental compliance.

• Common Uses: Automotive parts, hardware, industrial components.

3. Black Passivation

• Appearance: Matte or semi-gloss black.

• Properties:

  • Similar corrosion resistance to yellow passivation (72–96+ hours salt spray).

  • Achieved with chromate-based or organic black dyes.

• Common Uses: Military equipment, optical devices, automotive trim (for aesthetics).

4. Olive Drab / Green Passivation

• Appearance: Dark greenish-gray (military-style finish).

• Properties:

  • Originally developed for military applications (MIL-DTL-46001).

  • Excellent corrosion resistance (96+ hours salt spray).

  • Often contains hexavalent chromium, but alternatives exist.

• Common Uses: Defense, aerospace, outdoor equipment.

5. Trivalent Passivation (Non-Hexavalent, RoHS-Compliant)

• Appearance: Can be clear, blue, black, or olive drab depending on additives.

• Properties:

  • Environmentally friendly (no Cr⁶⁺).

  • Corrosion resistance varies (48–120+ hours depending on formulation).

• Common Uses: Electronics, medical devices, EU-regulated products.

6. Other Specialty Colors (Dyed Passivation)

• Some processes allow for dyed passivation layers, such as:

  • Red, blue, green, or purple (used for coding or aesthetics).

  • These are less common and may have reduced corrosion resistance.

Comparison Table

Key Considerations When Choosing a Color

• Corrosion Resistance Needed? (Yellow/Black/Olive offers better protection.)

• Aesthetic Requirements? (Black or dyed for appearance.)

• Environmental Regulations? (Trivalent for RoHS/REACH compliance.)

• Post-Treatment? (Some colors can be sealed or top-coated for extra protection.)