Dacromet vs Zinc Plating: Which Coating is Safer for High-Strength Bolts?

Key Features / Why It Matters

• Coating choice affects not just corrosion resistance, but reliability
• Zinc plating introduces hydrogen during processing
• High-strength bolts (10.9 / 12.9) are sensitive to hydrogen embrittlement
• Dacromet (zinc flake) is non-electrolytic and avoids this risk
• Coating selection can determine long-term performance

What Zinc Plating Does

Zinc plating is electroplating. An electric current deposits a thin layer of zinc onto the steel surface. It's cheap, it's common, and it gives fasteners a clean, bright finish.

For standard bolts in normal applications, it works fine.

The catch is the process itself. Electroplating involves acid cleaning and electrical current. Both can introduce hydrogen into the steel. For Grade 8.8 bolts, that's usually not a problem. For Grade 10.9 or 12.9, trapped hydrogen can lead to hydrogen embrittlement—delayed cracking that shows up days or weeks after installation, with no warning.

What Dacromet (Zinc Flake) Does

Dacromet is a different category. It's a zinc flake coating applied without electricity—usually dip-spin or spray, then heat-cured.

No electroplating means no hydrogen introduced. That's the key difference.

The coating itself is uniform, even on complex thread geometry. Corrosion resistance is comparable or better than zinc plating. But the real advantage for high-strength bolts is safety: the process doesn't set up the conditions for hydrogen embrittlement.

Applications

• Automotive structural assemblies
• Heavy machinery connections
• Steel structure projects
• Energy equipment (wind, solar)
• Outdoor or corrosion-prone environments

Where the Risk Shows Up

Hydrogen embrittlement doesn't happen during installation. It happens later.

A Grade 12.9 bolt gets zinc plated. It passes inspection. It installs fine. Then a week later, under preload, it cracks. No rust. No overload. Just a clean break.

That's hydrogen doing its work. The bolt was strong enough. The process was the problem.

Dacromet coatings avoid that failure mode entirely. Not because the coating is stronger, but because the process doesn't put hydrogen into the steel in the first place.

Specifications / Buyer Considerations

Zinc plating is still the right choice in plenty of cases:

• Grade 8.8 bolts or lower
• Applications with moderate loads
• Cost-sensitive projects
• When you can confirm the supplier performs de-hydrogenation baking

Dacromet becomes the better option when:

• Using Grade 10.9 or 12.9 bolts
• High preload or cyclic loading is involved
• Failure would be costly or dangerous
• Long-term reliability is the priority

What to ask suppliers:

• Is post-plating baking done (de-hydrogenation heat treatment)?
• How soon after plating is it done?
• Are there records of process control?

For Dacromet coatings:

• Confirm coating type (zinc flake system)
• Check consistency of application

Conclusion

Zinc plating and Dacromet both protect against corrosion. For standard fasteners, either can work.

For high-strength bolts—especially Grade 10.9 and 12.9—the coating process matters as much as the material. Zinc plating introduces hydrogen risk that needs post-process baking to control. Dacromet avoids that risk from the start.

In critical applications, the right coating isn't just about rust protection. It's about making sure the bolt you install today is still holding a year from now.

We supply high-quality, customizable fasteners to meet a wide range of project needs.

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