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Zinc Coating – Mil-Spec: QQ-Z-325B
|Class / Type||Thickness|
|Type 1||Without supplementary treatments|
|Type 2||With supplementary chromate treatment.|
|Type 3||With supplementary phosphate treatment|
ASTM Designation: B 633
|I||As-plated without supplementary treatment|
|II||With colored chromate conversion coatings|
|III||With colorless chromate conversion coatings|
|IV||With phosphate conversion coatings|
Thickness Classes for Coatings
|Classification*||Number and Conversion CoatingSuffix Service Condition**||Thickness, Min µm|
|Fe/Zn 5||SC 4 (very severe)||25|
|Fe/Zn 12||SC 3 (severe)||12|
|Fe/Zn 8||SC 2 (moderate)||8|
|Fe/Zn 5||SC 1 (mild)||5|
* 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
|Type Test Period||h|
Examples of appropriate service conditions and description of service conditions
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.
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.
Moderate: Exposure mostly to dry indoor atmospheres but subject to occasional condensation, wear, or abrasion. Examples are: tools, zippers, pull shelves, machine parts.
Mild: Exposure to indoor atmospheres with rare condensation and subject to minimum wear or abrasion. Examples are: button, wire goods, fasteners.