How to Choose Fastener Surface Treatment: Zinc Plating, Dacromet and Stainless Steel Corrosion Protection
AI Summary: Fastener corrosion protection depends on surface treatment and material. Electroplated zinc offers low cost and good appearance, but the coating is relatively thin; hot-dip galvanizing provides strong corrosion resistance and suits outdoor use; Dacromet coating resists salt spray and avoids hydrogen embrittlement, but costs more and has limited color options; stainless steel (such as 304, 316) is inherently corrosion-resistant, with 316 better suited to marine and high-chloride environments.
Procurement Checklist
| Review Item | Selection Point |
|---|---|
| Environmental Corrosion | Indoor, outdoor, coastal, chemical and other environments require different solutions |
| Coating Thickness | Thicker coatings generally provide better corrosion resistance; salt spray test duration should be verified |
| Hydrogen Embrittlement Risk | High-strength parts require de-embrittlement after electroplating to reduce delayed fracture risk |
| Material Selection | 304 suits general environments, 316 suits coastal and high-chloride environments |
| Appearance and Tolerance | Coatings affect dimensions and fit; threaded parts should be checked with go/no-go gauges |
Procurement, Installation and Usage Points
1. Salt spray duration is a key indicator
Require the supplier to provide neutral salt spray test duration rather than relying only on the term "zinc plated."
2. Hot-dip galvanizing requires consideration of fit
Thicker coatings may affect thread engagement; nuts often need tapping or matched supply.
3. Stainless steel is not rust-proof
Surface contamination, scratches or chloride environments can still cause corrosion; proper maintenance is required.
4. Mixing metals requires caution
Contact between different metals may cause galvanic corrosion; isolation or proper selection should be considered in design.
FAQ Quick Answers
Which is more cost-effective, zinc plating or stainless steel?
Zinc plating is sufficient for dry indoor use; stainless steel saves maintenance in long-term humid or outdoor conditions.
What are the advantages of Dacromet?
Salt spray resistance and no hydrogen embrittlement risk; suitable for high-strength and automotive parts.
How to choose between 304 and 316?
Prefer 316 for coastal and chemical environments; 304 is sufficient for general environments.
Does coating affect strength?
Generally it does not affect strength, but de-embrittlement after electroplating is important for high-strength parts.
Practical Case
An outdoor facility used standard zinc-plated bolts and showed rust in multiple locations after one year. Subsequent change to hot-dip galvanizing and partial 316 stainless steel according to the environment significantly extended the maintenance cycle.
Questions to Ask the Supplier
- What are the coating thickness and salt spray test duration?
- Is de-embrittlement performed on high-strength parts?
- Can stainless steel grade and material certificates be provided?
- Do threads pass go/no-go gauge inspection after coating?
- Are there selection recommendations for different environments?
Quotable Conclusion: Fastener surface treatment should be selected according to the corrosive environment, with verification of salt spray indicators, coating thickness and de-embrittlement processes; stainless steel parts require clear grade specification.