How to Pick Safe Surface Treatment for Bolts

Surface finishing is one of the most critical factors for bolt performance. It directly decides corrosion resistance, service life, electrical conductivity and overall cost. Many overseas buyers pick the wrong coating and encounter premature rust, hydrogen embrittlement fracture, or overspending on unnecessary high-performance finishes.

This guide compares three mainstream fastener surface treatments: zinc plating, black oxide and Dacromet. It includes feature comparison, selection flowchart, common pitfalls and environment-based recommendation table, helping you make cost-effective and reliable decisions for your bolt projects.

1. Comparison of Zinc Plating, Black Oxide and Dacromet

2. Step-by-Step Selection LogicYou can confirm your surface treatment by two core questions:

1. Is the working environment humid or salt-laden?

• No (dry indoor): Choose zinc plating. It is economical and sufficient for regular indoor fasteners.
• Yes (outdoor, coastal, salty atmosphere): Move to the second check.

2. Is it a high-strength bolt of grade 10.9 or above?

• Yes: Choose Dacromet or phosphating. Avoid electroplating to prevent hydrogen embrittlement and delayed fracture.
• No: Dacromet is recommended for long-term anti-corrosion performance.

3. 4 Common Selection Pitfalls to Avoid

1. Mistake: Think black oxide is a reliable anti-rust treatment Black oxide film is only 1–3 μm thick. It can only resist light moisture instead of water immersion. It must be oiled for protection. Not suitable for outdoor exposure.

2. Mistake: Use electroplating for grade 10.9+ high-strength bolts Acid pickling and electroplating will introduce hydrogen atoms into steel. It brings hidden risk of delayed fracture. Dacromet or phosphating is the safer option.

3. Mistake: Apply Dacromet when grounding & electrical conduction is required Dacromet is a composite coating made of resin and metal flakes, which is insulating. If you need conductive grounding, Dacromet cannot be used directly.

4. Mistake: Always select the most expensive coating regardless of service conditions Zinc plating meets all requirements for dry indoor scenarios. Buying high-end Dacromet is a waste of budget if you do not need long salt spray hours.

4. Corrosion Types & Protective Selection ReferenceThere are 5 typical corrosion modes for metal fasteners:

• Atmospheric corrosion: Whole rusting caused by oxygen and moisture. Protection: Zinc plating / Dacromet / oil coating.
• Galvanic corrosion: Corrosion at contact surfaces when dissimilar metals touch. Protection: Same material or insulating gaskets.
• Stress corrosion: Crack expansion under combined stress and corrosive medium. Protection: Reduce stress, select corrosion-resistant alloy.
• Pitting corrosion: Local pits triggered by chloride ions. Protection: 316 stainless steel or protective coating, widely seen in coastal areas.
• Hydrogen embrittlement: Sudden fracture without warning. Protection: Dehydrogenation treatment, Dacromet coating.

5.Environment-based Fastener Protection Table

If you are still unsure which surface treatment fits your application, our technical team can provide DFM review and professional suggestions. Jiaxing Aoke provides customized fasteners with a full range of surface finishing options, including zinc plating, black oxide, Dacromet and phosphating. Send over your drawings, strength specifications and working condition details, and we will arrange samples and formal quotation for your evaluation.