Zinc plating vs Dacromet: which coating for screws and bolts?
A straight comparison between Cr3+ zinc electroplating (our in-house service) and zinc flake systems such as Dacromet/Geomet.
Zinc plating vs Dacromet / zinc flake
Short answer: zinc plating for general fasteners, zinc flake for high grades and extreme salt-spray specs
Cr3+ zinc electroplating gives bright colour options (white, blue, yellow) at low per-piece cost — the default for general screws, nuts and bolts. Dacromet (zinc flake) is applied without electricity, so it carries virtually no hydrogen-embrittlement risk and reaches several hundred salt-spray hours, but costs more and comes only in matte silver-grey or black. Grade 10.9+ bolts that are zinc plated must be hydrogen de-embrittlement baked — a service we run in-house.
Zinc electroplating versus Dacromet comparison
| Decision factor | Cr3+ zinc electroplating | Dacromet / zinc flake |
|---|---|---|
| Principle | Electrolytic deposit + Cr3+ passivate | Dip-spin zinc-aluminium flake coating, oven-cured (non-electrolytic) |
| Typical thickness | About 5–12 µm | About 6–10 µm per coat |
| Colour options | White, blue, yellow iridescent — bright finish | Matte silver-grey or black |
| Typical salt spray | About 24–120 h (passivate/sealer dependent) | About 480–1,000 h (per coating-system spec) |
| Hydrogen embrittlement risk | Present for high-strength parts — managed by baking (ISO 4042) | Virtually none (no electrolytic or acid step) |
| Cost per piece | Lower — suits high volume | Higher; requires a specialist coater |
| Electrical conductivity | Conductive | Binder-based layer; less suited to electrical contacts |
| Typical use | General fasteners, decorative, indoor/moderate outdoor | Grade 10.9/12.9 bolts, automotive chassis and brake parts, high salt-spray specs |
How to choose
Zinc plating
Choose Cr3+ zinc plating for general fasteners that need corrosion protection plus an attractive colour at volume-friendly cost, with EU-export-ready Cr6-free passivation. For high-strength parts we run hydrogen de-embrittlement baking to standard.
Dacromet / zinc flake
Choose Dacromet/zinc flake when the customer or automotive spec demands several hundred salt-spray hours, or the part is grade 10.9+ where hydrogen embrittlement risk must be eliminated entirely.
Limits before putting it on the drawing
- We apply Cr3+ zinc plating with in-house baking; zinc flake needs a specialist coater — if your spec calls for it, we can review the spec and advise.
- Salt-spray hours are a standardised test figure, not real outdoor service life.
- Electroplated fasteners at grade 10.9 / ~320 HV and above should always specify baking per ISO 4042.
- Torque coefficients differ between the two systems — confirm with assembly before switching specs.
What to send the finisher
- 1Property class / hardness of the part and its material
- 2Reference standard, e.g. ISO 4042 (electroplated) or ISO 10683 (zinc flake)
- 3Colour, target thickness and required salt-spray hours
- 4Whether baking is required (send the grade and we can assess)
- 5Lot quantity/weight and samples for a trial run
Frequently asked questions
Do you offer Dacromet / zinc flake?
No. We apply Cr3+ zinc electroplating in-house and do our own hydrogen de-embrittlement baking, but we do not apply Dacromet or zinc-flake coatings — those need a specialist coater. If your spec calls for zinc flake we can review it and advise.
Which is cheaper for bulk fasteners?
Zinc electroplating is lower cost per piece and suits high-volume screws, nuts and bolts. Zinc flake costs more and requires a specialist line.
Do you bake grade 10.9 bolts against hydrogen embrittlement?
Yes. Electroplated fasteners at class 10.9 and above are hydrogen de-embrittlement baked to ISO 4042 in our own ovens.