Comprehensive Guide to Screw Surface Treatments: Zinc, Zinc-Nickel, Dacromet, Geomet, and Nickel Plating with Salt Spray Standards

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Screw Surface Treatment & Salt Spray Standard Guide｜Dongguan Dexin Metal Co., Ltd.

Release time：2026.07.31 Source：Dexin Metal Views：25

Surface treatment is essential for screws to prevent rust and extend service life. Different coatings offer different corrosion resistance. Below is a simplified guide of mainstream plating processes, salt spray resistance hours, and industry application standards for your reference.

Note: All salt spray data refers to neutral salt spray (NSS) test, no red rust within specified hours.

1.Main Surface Treatment Processes

1）Zinc Plating (Blue / Color / Black Zinc)

The most cost-effective and widely used surface treatment. Forms a protective zinc layer to prevent oxidation with optional colors.

Blue White Zinc: 48–72 hours salt spray resistance
Color Zinc: 72–96 hours salt spray resistance
Black Zinc: 96–120 hours salt spray resistance

Pros: Low cost, smooth surface, multiple color options.

Cons: Risk of hydrogen embrittlement, not suitable for high-strength bolts and harsh outdoor environments.

Application: Indoor furniture, home appliances, general electronic parts.

2）Zinc-Nickel Alloy Plating

High-grade electroplating treatment with excellent anti-corrosion performance.

Salt spray resistance: 480–1200 hours

Pros: Thin coating (no impact on thread fitting), low hydrogen embrittlement risk, available in black finish.

Cons: Higher cost.

Application: Automotive parts, outdoor precision hardware, new energy equipment.

3）Dacromet / Geomet Coating

Inorganic zinc-aluminum high anti-corrosion coating, the best choice for high-strength fasteners.

Dacromet: 500–1500 hours salt spray resistance
Geomet (Chromium-free): 480–1000 hours salt spray resistance

Pros: No hydrogen embrittlement, high temperature resistance, excellent coverage for complex threads, super corrosion resistance. Cons: Single color, poor wear resistance. Application: Automotive chassis, photovoltaic, wind power, coastal outdoor equipment.

4）Nickel Plating

Focus on beautiful appearance and electrical conductivity.

Salt spray resistance: 24–72 hours

Pros: Bright finish, good wear resistance and conductivity.

Cons: Ordinary nickel plating has limited anti-rust ability.

Application: Precision electronic accessories, decorative hardware parts.

2.Industry Salt Spray Standard Requirements

1）Furniture Industry

Indoor dry furniture: 48–72h (Blue/Color Zinc)
Kitchen & damp indoor furniture: 72–96h (Color/Black Zinc)
Outdoor garden furniture: ≥120h (Zinc-nickel / Dacromet)

2）Automotive Industry

Interior parts (seat, door panel): 48–72h
Exterior & chassis parts: ≥720h (Zinc-nickel / Dacromet / Geomet)

3）Electronic & Appliance Industry

Indoor & closed equipment: 48–72h
Outdoor electrical & charging equipment: ≥168h

4）Outdoor & New Energy Industry

Street lamps, fitness equipment, photovoltaic and wind power parts: ≥240h, prefer zinc-nickel alloy or Dacromet coating.

3.Quick Selection Tips

Indoor & cost-sensitive projects: Choose conventional zinc plating.
High-strength bolts (8.8/10.9/12.9 grade): Prefer Dacromet or zinc-nickel plating to avoid hydrogen embrittlement fracture.
Outdoor & coastal environment: Avoid ordinary zinc plating, select high-corrosion-resistance coatings.
Match the coating grade with actual usage scenario to save cost.