Zinc-nickel is what you use when 240 hours of salt spray is not enough: an 8–12 µm deposit with 12–15% nickel that gives 500–1000 hours, at two to three times the cost of plain zinc.
| Thickness | 8–12 µm |
|---|---|
| Alloy composition | 12–15% nickel in zinc |
| Salt spray | 500–1000 h to red rust (ASTM B117) |
| Max service temperature | ≈150 °C |
| RoHS / REACH | Compliant |
| Effect on dimension | 8–12 µm per surface — 16–24 µm across a diameter |
| Hydrogen embrittlement | Yes on high-strength steel — post-bake mandatory |
| Typical use | Marine housings, offshore hardware, automotive underbody, exposed fasteners |
Zinc corrodes into zinc oxide and zinc hydroxide, which are soluble in chloride environments and wash away, exposing fresh zinc. A zinc-nickel alloy corrodes into a denser, less soluble product that stays on the surface and slows the reaction. That is the whole mechanism behind the five-fold improvement in salt spray — not a thicker barrier, a better one.
The alloy also has better temperature resistance than pure zinc, roughly 150 °C against 120 °C, and it tolerates alkaline cleaning better. In an offshore or marine-adjacent plant, that combination is usually worth the extra cost.
| Property | Zinc-nickel | Zinc (trivalent) | Hot-dip galvanising | Stainless substitute |
|---|---|---|---|---|
| Thickness | 8–12 µm | 5–8 µm | 45–85 µm | n/a |
| Salt spray | 500–1000 h | 96–240 h | 500–1500 h | Inherent |
| Max temp | 150 °C | 120 °C | 200 °C | 300 °C+ |
| Dimensional effect | Moderate | Moderate | Severe — no fits | None |
| Cost index | 2.5–3.5× | 1.0× | 1.5× | 3–4× |
Exposed housings and hardware with long maintenance intervals.
Read →Housings that see salt spray and washdown.
Read →When the part itself should be stainless rather than coated.
Read →When the duty is indoor and the budget is the constraint.
Read →In salt-spray environments, yes: 500–1000 hours against 96–240 changes the maintenance interval by years. Indoors, it is money spent for nothing.
Yes. At 10 µm per surface the bore shrinks by 20 µm across the diameter, which is two standard tolerance bands. Mask the bore, or plate before final grinding.
Yes, and it is the usual replacement for cadmium coatings, which are prohibited.
It can, but it is pointless — stainless protects itself. Zinc-nickel is for carbon and low-alloy steel.
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