Standard zinc plating is the most common and cost-effective corrosion protection method for fasteners (bolts, screws, nuts, and threaded rods).
Author: Marisa
Standard zinc plating is the most common and cost-effective corrosion protection method for fasteners (bolts, screws, nuts, and threaded rods). Below are key details about this process and its suitability for fasteners.
Electroplating Method: Fasteners are submerged in a zinc electrolyte solution, and an electric current deposits a thin zinc layer (typically 5–25 µm).
Post-Treatment: Most zinc-plated fasteners receive a chromate conversion coating (passivation) to enhance corrosion resistance.
| Type | Appearance | Corrosion Resistance | Common Use Cases |
|---|---|---|---|
| Clear/Blue Zinc | Shiny metallic | Moderate (48–72h salt spray) | Indoor, dry environments |
| Yellow Zinc (Zinc Chromate) | Yellow iridescent | Good (96–144h salt spray) | Automotive, outdoor |
| Black Zinc | Matte black | Moderate (similar to clear zinc) | Decorative, military |
| RoHS Trivalent Zinc | Bluish/golden | Good (replaces hexavalent chrome) | Eco-friendly applications |
✔ Cost-Effective – Cheaper than nickel, chrome, or cadmium plating.
✔ Good Corrosion Resistance – With chromate passivation, resists white rust.
✔ Maintains Thread Tolerance – Thin coating (vs. hot-dip galvanizing) avoids fit issues.
✔ Aesthetic Flexibility – Clear, yellow, or black finishes available.
❌ Not for Extreme Environments – Less durable than hot-dip galvanizing or stainless steel in marine/chemical settings.
❌ Hydrogen Embrittlement Risk – High-strength fasteners (>1,000 MPa) may require baking (200°C for 4–24h) to remove hydrogen.
❌ Wear Resistance – Zinc is softer than nickel or chrome, so it can wear off in high-friction applications.
ASTM B633 (Standard for Zinc Electroplating on Steel)
ISO 4042 (Zinc plating for fasteners)
MIL-DTL-3200 (Military spec for zinc plating)
✅ General Construction (indoor/outdoor, non-coastal)
✅ Automotive (Non-Critical Parts)
✅ Electronics & Appliances
✅ Budget-Conscious Projects
Avoid Zinc Plating If:
The fastener will face saltwater, acids, or high temperatures (>120°C).
High fatigue strength is required (e.g., aerospace, heavy machinery).
Hot-Dip Galvanizing (Thicker, better corrosion resistance)
Mechanical Zinc Plating (No hydrogen embrittlement)
Dacromet/Geomet (Zinc flake coating, superior salt spray resistance)
Stainless Steel (No plating needed, naturally corrosion-resistant)
Standard zinc plating is the go-to choice for most fasteners due to its balance of cost, corrosion protection, and ease of application. For threaded rods in mild to moderate environments, clear or yellow zinc plating is sufficient. For harsher conditions, consider upgrading to hot-dip galvanizing or specialty coatings.