Zinc Plating Service
Resolute Precision Manufacturing coordinates electrodeposited zinc plating for steel precision machined components requiring corrosion protection beyond what black oxide provides. Zinc plating offers sacrificial anodic protection the zinc coating corrodes preferentially, protecting the base steel even where the coating is scratched or damaged. We deliver zinc plated parts with chromate conversion coating and full certification from a single purchase order. Request a QuoteHow Zinc Plating Protects Steel
Zinc plating provides corrosion protection through two mechanisms. First, the zinc deposit acts as a physical barrier between the steel substrate and the corrosive environment preventing moisture and oxygen from reaching the steel surface. Second, and more importantly, zinc provides sacrificial anodic protection. Zinc is more electrochemically active than steel when both metals are present in a corrosive environment, the zinc corrodes preferentially, sacrificing itself to protect the underlying steel. This means that even at scratches, cut edges, or damaged areas where the steel substrate is exposed, the surrounding zinc continues to protect it.
This sacrificial protection mechanism makes zinc plating significantly more effective than paint or non-sacrificial coatings for long-term corrosion protection on steel components.
Our Services
Chromate Conversion Coating on Zinc
Zinc plating is typically followed by a chromate conversion coating that improves the corrosion resistance of the zinc layer itself and provides additional appearance control. Three chromate options are standard:
- Clear (bright) chromate — thin, transparent coating; bright metallic appearance; standard corrosion resistance
- Yellow (iridescent) chromate — heavier chromate film; amber to yellow iridescent appearance; improved corrosion resistance over clear
- Black chromate — black chromate conversion followed by topcoat; matte black appearance; used where appearance and corrosion resistance are both required
Specifications
| Standard | ASTM B633 SC1/SC2/SC3/SC4, MIL-PRF-27418, and customer specifications |
| Deposit Thickness | SC1: 0.0001″ (light service); SC2: 0.0002″ (mild service); SC3: 0.0003″ (moderate service); SC4: 0.0005″ (severe service) |
| Chromate Finish | Clear (Type II), yellow iridescent (Type III), and black (Type IV) |
| Salt Spray Performance | SC1 clear: 12 hours; SC2 yellow: 96 hours; SC3 yellow: 120 hours; SC4 yellow: 200 hours (typical) |
| Dimensional Impact | 0.0002″–0.0005″ per side, depending on the specification; should be considered for threaded and mating features |
| Materials | Carbon steel and alloy steel; not recommended for stainless steel, aluminum, or copper alloys |
| RoHS Compliance | Trivalent chromate (Cr3+) available; compliant with RoHS and ELV directives |
| Documentation | Plating certification, coating thickness reports, and salt spray test data provided with finished parts |
| ISO | ISO 9001:2015; outside suppliers qualified under RPM’s approved vendor procedures |
Zinc Plating Applications
Zinc plating is the most widely used corrosion protection coating for steel machined components in moderate to severe environments:
- Fasteners — standard zinc yellow chromate finish on machine screws, bolts, and nuts for general industrial use
- Hydraulic and pneumatic fittings — corrosion protection on steel hydraulic components in wet environments
- Automotive components — zinc plating on chassis, underhood, and brake components per OEM specifications
- Industrial machinery hardware — hardware and brackets in outdoor or washdown environments
- Agricultural and construction equipment components — high-humidity and chemical exposure applications
Frequently Asked Questions
What is the difference between zinc plating and hot-dip galvanizing?
Electrodeposited zinc plating produces a thin, uniform, precise coating (0.0002″–0.0005″) suitable for precision machined components. Hot-dip galvanizing applies a much thicker coating (0.003″–0.005″) by immersion in molten zinc appropriate for structural steel and fabrications but not for threaded or precision-fit components.
Does zinc plating affect the dimensions of threaded parts?
Yes. Zinc plating builds 0.0002″ to 0.0005″ per surface. On external threads, this reduces the thread clearance. Common practice is to plate external threads before final inspection and internal threads after plating. We advise on the appropriate threading and plating sequence during quoting.
Is hex chromate (yellow zinc) RoHS compliant?
Traditional hexavalent chromate (Cr6+) is not RoHS compliant. Trivalent chromate (Cr3+) is available and provides comparable corrosion performance while meeting RoHS and ELV directive requirements. We specify trivalent chromate for all RoHS-sensitive programs unless hexavalent is specifically required
What corrosion resistance does yellow zinc provide?
Yellow zinc chromate (SC2 or SC3 per ASTM B633) typically provides 96 to 200 hours to white rust in salt spray testing per ASTM B117. This is appropriate for moderate industrial environments. For severe or marine environments, electroless nickel or zinc-nickel alloy plating provides substantially better performance.