Zinc Coating – Mil-Spec: QQ-Z-325B
|Type 1||Without supplementary treatments.|
|Type 2||With supplementary chromate treatment.|
|Type 3||With supplementary phosphate treatment.|
ASTM Designation: B 633
Electrodeposited Coatings of Zinc on Iron and Steel.
As-plated without supplementary treatment
With colored chromate conversion coatings
With colorless chromate conversion coatings
With phosphate conversion coatings
Thickness Classes for Coatings:
Classification* Number and Conversion CoatingSuffix Service Condition**Thickness, Min µm
SC 4 (very severe)
SC 3 (severe)
SC 2 (moderate)
SC 1 (mild)
* Iron or steel with zinc electroplate. Numeral indicates thickness in micrometres.
** Where service conditions are valid only for coatings with chromate conversion coating. Type II for SC 4 and SC 3 and Type III for SC 2 and SC 1.
Corrosion Resistance Requirements:
TypesTest Period, h
Examples of appropriate service conditions and description of service conditions
SC 4 – Very Severe: Exposure to harsh conditions, or subject to frequent exposure to moisture, cleaners, and saline solutions, plus likely damage by denting, scratching, or abrasive wear. Examples are: plumbing fixtures, pole line hardware.
SC 3 – Severe: Exposure to condensation, perspiration, infrequent wetting by rain, and cleaners. Examples are: tubular furniture, insect screens, window fittings, builder’s hardware, military hardware, washing machine parts, bicycle parts.
SC 2 – Moderate: Exposure mostly to dry indoor atmospheres but subject to occasional condensation, wear, or abrasion. Examples are: tools, zippers, pull shelves, machine parts.
SC 1 – Mild: Exposure to indoor atmospheres with rare condensation and subject to minimum wear or abrasion. Examples are: button, wire goods, fasteners.