Screw Surface Treatment Guide: Differences Between Zinc Plating, Black Oxide, Dacromet, and Corrosion Resistance
- 翰君 陳
- 2 days ago
- 3 min read
In many industrial applications, the durability of screws is not determined only by material and strength—surface treatment also plays a critical role.
For example, a carbon steel screw without any treatment may rust quickly. However, with proper surface treatment, its corrosion resistance can be significantly improved.
Different surface treatments vary greatly in corrosion resistance and application environments. Therefore, when selecting screws, surface treatment must be considered alongside size and strength.
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1. Why Do Screws Need Surface Treatment?
Surface treatment mainly serves three purposes:
1. Prevent Rust
Metals exposed to air and moisture will oxidize over time. Surface treatment helps extend service life.
2. Improve Corrosion Resistance
In outdoor, humid, or salt spray environments, corrosion resistance is essential.
3. Improve Appearance and Friction
Some treatments provide a more uniform color or reduce friction, making assembly smoother.
Many people assume all surface treatments perform similarly, but in reality, their corrosion resistance can vary significantly.
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2. Common Types of Screw Surface Treatments
Common surface treatments can be summarized as follows:
Surface Treatment | English Name | Corrosion Resistance | Typical Applications |
Black Oxide | Black Oxide | Low | Indoor equipment |
Zinc Plating | Zinc Plating | Medium | General industry |
Nickel Plating | Nickel Plating | Medium | Decorative parts |
Dacromet | Dacromet | High | High corrosion environments |
Zinc Flake | Zinc Flake Coating | High | High salt spray environments |
Passivation | Passivation | Medium to High | Stainless steel parts |
Anodizing | Anodizing | Medium | Aluminum parts |
Important note:Stainless steel is a material, not a surface treatment.
For stainless steel screws, the common post-treatment is passivation.
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3. How Much Do Surface Treatments Differ in Corrosion Resistance?
Corrosion resistance is typically evaluated using the Salt Spray Test.
Approximate performance:
Surface Treatment | Salt Spray Resistance |
Black Oxide | A few hours |
Zinc Plating | ~48–96 hours |
Dacromet | ~500–1000 hours |
Zinc Flake Coating | ~600–1000 hours |
Passivation | Depends on material & process |
Anodizing | Depends on coating thickness & environment |
Longer salt spray test duration indicates better corrosion resistance.
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4. Why Do Zinc-Plated Screws Show “White Rust”?
White powder sometimes appears on zinc-plated screws. This is called:White Rust
It is formed when zinc reacts with moisture.
This means:The zinc layer is being consumed, not the base metal rusting.
Zinc plating works on a sacrificial protection principle—the zinc corrodes first to protect the steel.
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5. Why Can’t High-Strength Screws Be Plated Freely?
Electroplating may introduce a risk called:Hydrogen Embrittlement
This causes the metal to become brittle and more likely to fracture under stress.
Special caution is required for:
High-strength screws
Load-bearing components
Therefore, surface treatment selection must consider process risks, not just corrosion resistance.
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6. Zinc Plating vs Zinc-Nickel vs Zinc Flake
Treatment | English | Characteristics | Corrosion Resistance |
Zinc Plating | Zinc Plating | Most common electroplating | Medium |
Zinc-Nickel | Zinc Nickel Plating | High corrosion resistance plating | High |
Zinc Flake | Zinc Flake Coating | Non-electroplated coating | High |
Key differences:
Zinc Plating → Low cost, general use
Zinc-Nickel → Improved corrosion resistance
Zinc Flake → No hydrogen embrittlement risk, high corrosion resistance
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7. What Are Delta Protekt and Geomet?
These are brand systems of Zinc Flake coating.
Zinc Flake = technology
Delta Protekt / Geomet = brands
In addition to corrosion protection, they also help control friction for more stable fastening.
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8. What Is Passivation? Why Is It Used for Stainless Steel?
Passivation is commonly used for stainless steel.
It does not add a coating but uses chemical treatment to form a more stable protective layer.
Common Types:
1. Citric Acid Passivation
Environmentally friendly
No heavy metals
Increasingly popular
2. Nitric Acid Passivation
Traditional method
Stable process
Long history of use
In simple terms:
Passivation enhances the natural corrosion resistance of stainless steel.
--- 9. Why Is Anodizing Used for Aluminum?
Anodizing is mainly applied to aluminum:
Increases hardness
Improves corrosion resistance
Allows coloring
Common in appearance parts and lightweight designs.
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10. How to Choose Based on Environment?
Environment | Recommended Treatment |
Indoor equipment | Black Oxide |
General industry | Zinc Plating |
High corrosion environment | Dacromet / Zinc Flake |
Stainless steel parts | Passivation |
Aluminum parts | Anodizing |
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11. Why Choose Sheng Fong Precision?
Sheng Fong Precision provides a wide range of machine screws and industrial components, and helps customers select the most suitable surface treatment based on different application environments—preventing issues such as rust, thread damage, or failure.
LINE: @s9000