Fastener Coatings Compared: Zinc, Zinc-Nickel and Passivated Stainless
Corrosion protection is a coating decision made long before the first raindrop. The three mainstream choices trade cost, protection and process risk.
Bottom line: for most Surface Treatment applications the decision comes down to load, environment and assembly method — the Surface Treatment guide walks through the selection.
Electroplated zinc: the budget baseline
Zinc sacrificially protects steel and takes color passivates (blue, yellow, black) cheaply. Unsealed blue zinc survives ~96–200 h of neutral salt spray; sealed systems push higher. Watch hydrogen embrittlement on hardened parts — baking after plating is not optional above 1000 MPa.
Zinc-nickel: the automotive workhorse
Alloys with 12–15% nickel deliver 480–720 h salt spray unsealed, better galvanic compatibility with aluminum, and stable friction coefficients — which torque-controlled lines love. It is the default spec for EV and chassis hardware exposed to road salt.
Stainless with proper passivation
For permanent exposure or wash-down, A2/A4 stainless passivated per ISO 3506 sidesteps coating life questions entirely — at material cost and with galling precautions.
Decide with the mission profile
Match coating to exposure hours, then verify friction data for your torque spec. Topprecision plates in-house partners supply full salt-spray reports per lot, and we publish K-factor ranges per finish so your torque windows survive the coating change.
Fastener material comparison
| Material | Tensile (MPa) | Density (g/cm³) | Best for |
|---|---|---|---|
| Steel 8.8 | 800 | 7.85 | General structural, machinery |
| Steel 12.9 | 1220 | 7.85 | Weight-critical, tooling |
| Stainless 304 (A2-70) | 700 | 7.93 | Indoor, food, corrosion-resistant |
| Stainless 316 (A4-80) | 800 | 7.98 | Marine, coastal, chloride |
| Aluminum 7075-T6 | 570 | 2.81 | Weight-critical aerospace |
| Titanium Grade 5 | 900 | 4.43 | Aerospace, medical, high cost |
Need help selecting the right fastener material?
Toprecision cold-heads and CNC-turns fasteners in steel (4.6–12.9), stainless 304/316/410, aluminum 6061/7075, titanium Grade 5 and engineering plastics. Send the service environment and load requirement — we will recommend the material and grade with tensile test data. Request material selection support.
