ASTM B633
Standard Specification for Electrodeposited Coatings of Zinc on Iron and Steel
Specifies electrodeposited zinc coatings on iron and steel, including service-condition thickness and supplementary-treatment classifications.
What ASTM B633 specifies
ASTM B633 is the common North American drawing specification for zinc electroplating on steel. Service conditions SC1 through SC4 require minimum local zinc thicknesses of 5, 8, 13, and 25 µm. The coating type identifies the supplementary finish: Type I as-plated, Type II colored chromate, Type III colorless chromate, Type IV phosphate, Type V colorless passivate, and Type VI colored passivate. The purchaser should state service condition, type, significant surfaces, appearance, and any hydrogen-embrittlement requirements. Corrosion performance depends on both zinc thickness and the selected conversion coating or passivate.
ASTM B633 types and classes
Every designation the document defines, with the thickness it requires and the tests it imposes.
| Designation | Meaning | Thickness | Requirement / test |
|---|---|---|---|
SC1 | Mild service | ≥ 5 µm ≥ 0.2 mil | Thickness and adhesion per specification |
SC2 | Moderate service | ≥ 8 µm ≥ 0.31 mil | Thickness and adhesion per specification |
SC3 | Severe service | ≥ 13 µm ≥ 0.51 mil | Thickness, adhesion, and corrosion per specified type |
SC4 | Very severe service | ≥ 25 µm ≥ 0.98 mil | Thickness, adhesion, and corrosion per specified type |
Type I | As-plated zinc without supplementary treatment | — | Appearance and applicable coating tests |
Type II | Colored chromate conversion coating | — | Corrosion resistance per ASTM B117 |
Type III | Colorless chromate conversion coating | — | Corrosion resistance per ASTM B117 |
Type IV | Phosphate conversion coating | — | Applicable supplementary-treatment tests |
Type V | Colorless passivate | — | Corrosion resistance per ASTM B117 |
Type VI | Colored passivate | — | Corrosion resistance per ASTM B117 |
Tests and the drawing call-out
Tests the document imposes
- Coating thickness
- Adhesion
- Corrosion resistance by ASTM B117 where applicable
- Visual examination
- Hydrogen embrittlement relief when required
How to cite it
Drawing call-out
ZINC PLATE PER ASTM B633, SC<1|2|3|4>, TYPE <I|II|III|IV|V|VI>Angle brackets mark the choices the drawing must make; every finish page shows a completed example.
Finishes specified to ASTM B633
ASTM B633 — frequently asked
What is ASTM B633 SC2 thickness?
SC2 requires a minimum local zinc thickness of 8 µm on significant surfaces.
What is the difference between ASTM B633 Type II and Type III?
Type II is a colored chromate supplementary finish; Type III is colorless chromate. The type is separate from the SC thickness class.
How should ASTM B633 be called out?
State the specification, service condition, and supplementary-treatment type, then add color, significant surfaces, masking, or embrittlement-relief requirements as needed.
ASTM B633 is copyrighted by ASTM International. This page explains the document so a drawing can be read; it does not reproduce the standard. Purchase the current edition from the publisher. Official source ↗