Zinc plating vs zinc-nickel: when is the upgrade worth paying for?
We plate Cr3+ zinc in-house and we do not have a zinc-nickel bath. This page explains when a spec should genuinely call for Zn-Ni and when plain zinc is enough.
Zinc plating vs Zinc-nickel
Short answer: zinc-nickel buys corrosion and heat resistance, zinc buys cost per piece
Zinc-nickel is an alloy layer containing roughly 12–16 % nickel. At the same thickness it protects better than pure zinc, it keeps protecting after sustained heat, and it sits closer to aluminium electrochemically, which is why automotive specifications reach for it. Cr3+ zinc plating gives the colour range, runs easily in volume and costs clearly less per piece, which is why it remains the default for general fasteners. Both are electrolytic, so both need a de-embrittlement bake on high-strength parts. We offer zinc only — there is no zinc-nickel line here.
Zinc plating versus zinc-nickel
| Decision factor | Cr3+ zinc plating (our line) | Zinc-nickel (not offered here) |
|---|---|---|
| Type of layer | Pure zinc deposit with a Cr3+ passivate | Zinc-nickel alloy at roughly 12–16 % nickel, passivated and usually sealed or topcoated |
| Standards usually quoted | ISO 4042, ISO 2081, ASTM B633 | ISO 4042 alloy designations, ASTM B841, ASTM F1941 for fasteners, DIN 50979, ISO 19598 |
| Typical thickness | About 5–12 µm | About 5–12 µm as well, but more protection for the same thickness |
| Typical salt-spray behaviour | Tens of hours up to a couple of hundred before white rust, depending on passivate and sealer | Supplier system data commonly runs from several hundred hours towards about a thousand before red rust |
| After heat exposure | The passivate degrades relatively quickly under sustained heat | Holds its corrosion performance better after under-bonnet style heat |
| In contact with aluminium | A larger potential difference drives galvanic attack at the joint | A smaller difference, which is why it is chosen for assemblies onto aluminium |
| Hydrogen embrittlement risk | Present — high-strength parts must be baked (we bake in-house) | Also present and often higher, because bath current efficiency is lower; baking is equally required |
| Friction on tightening | Different from other systems; specify a friction modifier if torque is controlled | Different again, and usually specified together with a friction-modifying topcoat |
| Cost and process control | Lower and simpler to run in volume | Significantly higher — the nickel content of the deposit must be controlled and nickel-bearing effluent managed |
| Parts it suits | General fasteners, indoor, semi-exposed or painted-over service | Automotive specs with high corrosion requirements, under-bonnet parts, and assemblies onto aluminium |
| Who can run it | In-house here, with de-embrittlement ovens on site | We have no Zn-Ni bath; this goes to a plater who runs that line |
How to choose
Zinc plating
Choose Cr3+ zinc plating for general fasteners used indoors, semi-exposed or under paint, where the colour range matters and cost per piece has to work in volume. High-hardness parts get their de-embrittlement bake in the same building.
Zinc-nickel
Choose zinc-nickel when the customer specification names the alloy layer outright, when the part must survive high corrosion requirements combined with sustained heat, or when a steel fastener bolts directly into aluminium. That work goes to a plater with a Zn-Ni bath, not to us.
Limits before this goes on the drawing
- We have no zinc-nickel line and will not plate plain zinc against a Zn-Ni specification without written approval from the drawing owner.
- Salt-spray hours are a laboratory test result, not a service-life prediction, and the figures quoted for Zn-Ni systems come from the chemistry supplier — they are not values we guarantee.
- Both processes are electrolytic, so parts at roughly property class 10.9 and above need a de-embrittlement bake either way; zinc-nickel is not exempt.
- Switching between zinc and zinc-nickel changes the tightening torque; re-check it with the assembly engineer and consider a friction-modifying topcoat.
- The designation on the drawing matters more than the name — send the full coating code, because one code can fix the metal, the thickness, the passivate type and the sealer at once.
- The only quality system we hold is ISO 9001:2015. Vehicle-maker requirements and source approvals are things that sector imposes and the buyer must verify with the spec owner.
What to send us for review
- 1The full coating designation exactly as the drawing writes it, with the standard it references
- 2Part type, thread size, material and property class or hardness
- 3Service conditions: temperature seen, contact with aluminium, coastal exposure
- 4The corrosion hours the spec requires and the report you need with the parts
- 5Lot quantity or weight, plus sample pieces for a trial run
Frequently asked questions
Do you offer zinc-nickel plating?
No. There is no zinc-nickel bath in our plant. Work specifying Zn-Ni has to go to a plater who runs that line. We provide Cr3+ zinc plating with hydrogen de-embrittlement baking for small parts in bulk.
Can plain zinc be substituted for zinc-nickel?
Not as a shop decision. It is a different deposit, a different code on the drawing and a different level of corrosion protection. Any substitution needs written approval from the drawing owner.
Why does automotive work ask for Zn-Ni so often?
Because the layer keeps protecting after sustained heat and reduces galvanic attack where a steel fastener meets aluminium. Those are requirements that sector writes into its own specifications, and the buyer should confirm them with the spec owner.
Is zinc-nickel free of hydrogen embrittlement risk?
No. It is still electroplating, and the bath typically runs at lower current efficiency. High-strength parts need the same de-embrittlement bake as they would after zinc plating.