Zinc and nickel are the two most common plating choices for steel parts. Zinc plating is cheap, protects through sacrificial corrosion (zinc corrodes instead of steel). Nickel plating is more decorative, better corrosion protection, harder surface — but more expensive. This guide covers when each makes sense.
Zinc plating: The steel part is immersed in a zinc electrolyte bath with an electrical current. Zinc ions are reduced onto the part surface. The zinc layer protects through sacrificial corrosion — if the plating is scratched and steel exposed, the adjacent zinc corrodes preferentially, protecting the steel.
After plating, a chromate conversion (chromate dip) is typically applied:
Nickel plating: Two main methods:
| Property | Zinc + chromate | Electroless nickel |
|---|---|---|
| Typical thickness | 5-25 μm | 10-50 μm |
| Hardness (as plated) | 60 HV | 400-550 HV |
| Hardness (after heat treat) | n/a | 800-1000 HV (wear-hard) |
| Salt spray (bare) | 8-96 hrs to white rust | 200-1000 hrs (depends on P) |
| Protection mechanism | Sacrificial (zinc corrodes first) | Barrier (physical coating) |
| Uniformity on complex geometry | Poor (deeper recesses get thinner) | Excellent (equal everywhere) |
| Surface finish | Matte silver | Bright silver, mirror-like |
| Color options | Silver, yellow, black (chromate) | Silver only |
| Cost (% of part) | +$0.50-2 per part | +$2-8 per part |
| Lead time | 1-2 days | 3-7 days |
Bolts, nuts, washers in general industrial use. Cost per kg of protection is unbeatable. Indoor or sheltered service.
Agricultural equipment, construction hardware, general-purpose outdoor gear. The sacrificial behavior of zinc protects steel even when plating is partially damaged.
Sheet metal brackets, electrical enclosures, HVAC ducting. Zinc covers large areas cost-effectively.
Zinc is anodic to aluminum — in some assemblies this creates galvanic corrosion. For zinc parts contacting aluminum in humid environment, consider isolation or switch to EN.
Uniform coating thickness on interior surfaces. After heat treatment, EN approaches tool-steel hardness — excellent wear resistance.
EN deposits equal thickness regardless of shape. For parts with tight-tolerance internal features, EN maintains dimensional accuracy that electrolytic zinc cannot.
EN with high phosphorus (10-12%) resists corrosion better than zinc+chromate. For equipment in marine or chemical environments, EN is superior.
EN is FDA-approved for indirect food contact. Zinc plating has restrictions. For food processing equipment steel parts, EN is the safer choice.
Gun slides, piston rods, cam followers. EN after heat treatment is extremely hard and low-friction — better than base steel for sliding applications.
When specifying zinc plating, include:
When specifying electroless nickel, include:
The chromate passivation step after zinc plating used to be hexavalent chromium (Cr⁶⁺) — toxic and regulated. Modern ROHS-compliant zinc plating uses trivalent chromium (Cr³⁺) passivation.
Always specify trivalent unless you have a specific aerospace/military reason for hex. Confirm with your plating vendor — some older shops still default to hex.
Email [email protected] with your drawing and environment. For general hardware, zinc + trivalent chromate is cost-effective. For precision, wear, or complex geometry, electroless nickel. We specify and coordinate both.
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