Zinc Electroplating

Zinc electroplating is one of the most cost-effective ways to prevent rust. It protects sacrificially, so if the surface gets scratched, the zinc corrodes first and the steel underneath stays protected.

The chromate (or passivate) forms a passive layer over the zinc that delays the white corrosion bare zinc develops on its own.

Typical coating thickness runs 0.0002" to 0.0005" (5–12 microns), depending on the specification.

Clear/blue zinc, certified to ASTM B633 Type III, plated with a non-hexavalent (trivalent) chromate which means no Cr(VI) in your supply chain. The finish carries an iridescent-to-blue sheen.

ASTM B633 Type II yellow is currently in testing.

ASTM B633 is the standard specification for zinc coatings on iron and steel. It defines coating thickness by service condition class, and the type of chromate conversion coating applied over the zinc.

Type III is a colorless (clear/blue) chromate. It requires a minimum of 12 hours of salt spray testing — an accelerated corrosion test that measures how well a finish holds up. Our most recent testing exceeded 24 hours.

While all types of zinc plated parts will have similar corrosion protection, the processes can use different chemistries that don't all look alike.

The common acid zinc process will level as it plates: its additives fill the microscopic texture of the steel, so the finish comes out smoother than the surface it plates to.

Ours doesn't level, instead it closely replicates the surface it's given. Shinier machined metal surfaces will plate brighter, and rougher/textured, hot- or cold-rolled mill finishes will have a more satin lustre.

Our process tends to plate a little bit more evenly, so recesses, threads, and blind areas will have hold closer to the same thickness and corrosion protection everywhere.

Type II is typically a yellow/gold chromate that requires a minimum of 96 hours of white corrosion protection. Hexavalent chromate used to be the only option for this level of coverage, but now many trivalent chromate products combined with sealers can offer the same protection without the health and environmental hazards of hexavalent chromium.

Type II trivalent chromates can also come in a clear/blue.

OEM specifications can often add requirements beyond the ASTM standard. That can mean an approved-source-only status for the plating facility, a specific thickness, a particular chromate type, and/or salt spray testing certified to that part.

We can tell you what the specification on your drawing requires and whether we can meet them.