Electroplating & Metal Plating: Process Selection, Costs & Sourcing Guide

Electroplating deposits a metallic coating (0.5–250µm) onto a part through electrolysis. It's one of the most specified secondary operations in custom manufacturing — yet it's routinely under-specified in RFQs, leading to quality escapes, corrosion failures, and hydrogen embrittlement risks that can cause catastrophic field failures. The difference between a $0.06/part zinc plate and a $0.25/part zinc plate might be the difference between 96 and 500 hours of salt spray protection.

This guide covers every major plating process, real cost benchmarks, specification writing best practices, and the rack vs. barrel decision that determines 50–75% of your plating cost.

Plating Process Selection Guide

Zinc Plating — Corrosion Protection Standard

• What it does: Sacrificial protection — zinc corrodes preferentially to steel, protecting the substrate even when the coating is scratched
• Thickness range: 5–25µm (most common: 8–12µm for general hardware)
• Salt spray (ASTM B117): 8µm clear Cr3+: 96–120 hrs to white rust | 12µm + trivalent chromate + topcoat: 500+ hrs
• Color options: Clear (blue), yellow (gold), black, olive drab — all trivalent chromate (RoHS compliant)
• Cost (barrel, 5,000 pcs): Small fasteners $0.03–0.15/pc | Brackets $0.20–0.80/pc
• Cost (rack, 5,000 pcs): Small parts $0.15–0.50/pc | Large parts (>200mm) $0.50–3.00/pc
• Spec: ASTM B633 — specify Type (chromate color), Class (Fe/Zn thickness), and service condition (SC1–SC4)

Nickel Plating — Decorative & Engineered

• Bright nickel (electrolytic): 10–20µm, HV 500–600 hardness, mirror-like finish. Used for consumer hardware, faucets, automotive trim
• Electroless nickel (EN): Deposits uniformly regardless of geometry (±10% vs ±50% for electrolytic). HV 500 as-plated → HV 1000+ after 400°C bake. The precision plating process
• Sulfamate nickel: Low-stress deposit, 25–250µm thickness. Mold repair, engineering builds
• Cost (bright, rack): $0.30–1.50/part | EN: $0.50–4.00/part (higher chemistry cost)
• When to choose EN: Complex geometry with blind holes, internal threads, deep recesses. Electrolytic nickel plates thin in recessed areas (Faraday cage effect); EN plates everywhere the solution reaches
• Spec: ASTM B689 (electrolytic) | ASTM B733 (EN, specify SC1–SC4 service condition and type by phosphorus content)

Chrome Plating — Decorative & Hard

• Decorative (0.25–1.0µm): Always over nickel undercoat (15–25µm Ni + thin Cr). Bright, reflective, blue-white appearance
• Hard chrome (25–250µm): Direct to steel. HV 850–1050. Wear surfaces — piston rods, cylinder bores, hydraulic shafts, mold surfaces
• Cost (decorative Ni+Cr): $0.50–3.00/part (small) | $3.00–12.00/part (large decorative)
• Cost (hard chrome, per dm²): $0.80–2.50 for 25–50µm | $1.50–4.00 for 100–250µm
• Regulatory warning: Hard chrome uses Cr6+ (hexavalent chromium, classified carcinogen). EU REACH is phasing it out. Consider electroless nickel or HVOF thermal spray as alternatives for new designs
• Spec: ASTM B177 (decorative) | AMS 2460 / ASTM B650 (hard chrome)

Tin Plating — Solderability & Food Safety

• Thickness: 3–15µm (connectors) | 15–30µm (food contact)
• Why tin: Excellent solderability retained >12 months, RoHS compliant, low contact resistance, FDA food-contact acceptable
• Bright vs. matte: Bright tin grows tin whiskers — metallic filaments that cause short circuits. Matte tin (with post-reflow or nickel undercoat) is mandatory for aerospace, military, and high-reliability electronics per GEIA-STD-0005-2
• Cost: $0.05–0.30/part (barrel) | $0.15–0.80/part (rack)
• Spec: ASTM B545

Gold & Silver — Electrical & High-End

• Gold (0.5–2.5µm): Over nickel strike. <0.5mΩ contact resistance. No oxidation. Required for high-reliability connectors (mil-spec, medical, telecom)
• Silver (3–15µm): Highest electrical conductivity of any plating. Busbars, RF connectors, high-current contacts
• Gold cost: $1.00–8.00/part (gold at ~$87/gram, March 2026)
• Cost reduction: Selective plating — mask non-contact areas to reduce precious metal usage 60–80%

Rack vs. Barrel: The Decision That Controls 50–75% of Plating Cost

Barrel Plating

• How: Parts tumble in a perforated barrel in the plating bath. Current flows through part-to-part contact
• Best for: Small parts (<150mm), volumes >500 pcs, parts that tolerate tumbling contact
• Cost advantage: 50–75% cheaper than rack (no fixturing labor)
• Trade-offs: Thickness uniformity ±30–40%, surface contact marks, parts must survive tumbling without deformation
• NOT for: Polished surfaces, thin walls (<0.5mm), protruding features, tight flatness requirements

Rack Plating

• How: Parts individually fixtured on conductive racks with clips/hooks
• Thickness control: ±10–15% (standard) | ±5% with auxiliary anodes and shields
• Key spec: Define rack mark locations on your drawing — ideally on non-functional surfaces. This is the #1 cosmetic complaint in rack plating

Cost Example: Zinc Plating a Steel Bracket (60×40×20mm)

• Barrel (5,000 pcs): Offshore $0.06/part | US domestic $0.18–0.30/part
• Rack (5,000 pcs): Offshore $0.25/part | US domestic $0.65–1.20/part
• Decision rule: If barrel quality meets your functional requirements, always barrel. The savings compound at volume

How to Write a Plating Specification That Gets Accurate Quotes

Vague specs produce vague quotes and inconsistent quality. Include all of these in your RFQ:

1. Plating type + thickness + spec: "Zinc per ASTM B633, Type II, Class Fe/Zn 12" (12µm min, yellow trivalent chromate)
2. Measurement method: XRF for spot checks | Coulometric (destructive) for referee. Specify measurement point locations
3. Significant surfaces: Mark on drawing which surfaces must meet full thickness spec. Recessed areas can have 40–50% less per ASTM standards
4. Adhesion test: ASTM B571 Section 4.1 (tape test) or heat-quench (190°C × 1hr, quench, inspect for blistering)
5. Hydrogen embrittlement baking: CRITICAL for hardened steel >HRC 31. Specify 190–220°C for 4–24 hours within 4 hours of plating, per ASTM B850. Failure causes delayed brittle fracture
6. Salt spray (ASTM B117): Specify hours to white corrosion AND red corrosion separately. Example: "96 hrs min to white, 500 hrs min to red"
7. RoHS compliance: Mandate trivalent (Cr3+) chromate passivation. Update legacy drawings that reference hexavalent
8. Appearance standard: Provide limit samples (accept/borderline/reject) for decorative plating. Specs alone can't capture color and brightness expectations

Plating vs. Alternatives: When to Choose Something Else

Zinc Plate vs. Hot-Dip Galvanize

• Zinc plate (5–25µm): Precise thickness, smooth finish, close-tolerance parts
• Hot-dip galvanize (45–85µm): 3× thicker, 30+ year outdoor life, but rough surface and ±100µm dimensional change. Not for precision parts
• Rule: Indoor/controlled → zinc plate. Outdoor/structural → galvanize

Electroless Nickel vs. Hard Chrome

• EN: Uniform thickness on complex geometry, no Cr6+, hardness up to HV 1000+ with heat treat. Growing as hard chrome replacement
• Hard chrome: Better raw wear resistance for sliding applications, cheaper per µm. But Cr6+ regulatory pressure mounting
• Trend: EU REACH is driving EN + PVD to replace hard chrome. Design new products accordingly

Plating vs. Powder Coating

• Zinc plate: 5–25µm, metallic, dimensionally precise, electrically conductive
• Powder coat: 50–150µm, any color, UV resistant, but adds thickness and is non-conductive
• Best of both: Zinc + powder coat duplex system for maximum outdoor protection. Zinc sacrificially protects any coating damage. Standard on outdoor furniture, guardrails, agricultural equipment

Landed Cost: Plated Parts from Offshore Suppliers

Typical steel stamped bracket, zinc plated and passivated (Qty 10,000):

• Part (stamped, FOB): $0.45
• Zinc plate (barrel, 12µm + Cr3+): $0.06
• Packing (bulk box, VCI): $0.02
• Ocean freight: $0.03
• US duty (Vietnam origin): 0% — no Section 301 surcharge
• Landed: ~$0.58/part
• US domestic: $1.45–2.20/part
• Savings: 60–74%

The same part from China adds 25% Section 301 tariff on the finished part value, making Vietnam the clear cost winner for plated metal parts.

5 Plating Sourcing Mistakes That Cost You Money (or Worse)

1. Skipping hydrogen embrittlement baking on hardened steel: The most dangerous plating defect. Hardened steel (>HRC 31) absorbs hydrogen during plating. Without post-plate baking, parts develop delayed brittle fracture — sometimes weeks after installation. Always specify ASTM B850 baking for springs, fasteners, and heat-treated parts.
2. Using hex chrome specs on RoHS products: Legacy drawings may call for "yellow chromate" (Cr6+). Update to trivalent chromate — equal or better salt spray, and you avoid RoHS/REACH compliance issues at the border.
3. Not defining significant surfaces: If every surface is "significant," the plater guarantees full thickness everywhere including deep recesses — dramatically increasing cost. Mark your drawing with significant vs. non-significant zones.
4. Barrel plating parts that need rack: Polished surfaces, thin walls, protruding features, and tight flatness specs are incompatible with tumbling. The cost savings of barrel aren't worth a 15% reject rate.
5. Not requiring thickness measurement reports: Every shipment should include XRF thickness data at specified measurement points. A plater who won't provide this data isn't one you should trust.