ASTM F1941 – Coating Properties
ASTM F1941 establishes the application, performance, and dimensional requirements for electrodeposited coatings on threaded fasteners with Unified Inch Screw Threads. The specification covers various coating materials—including zinc, cadmium, and zinc alloys—while defining standards for minimum local thickness and supplemental finishes such as hexavalent chromates or non-hexavalent passivates. A primary technical focus of this standard is the mitigation of hydrogen embrittlement risks, particularly for case-hardened fasteners or those with a hardness of 40 HRC or higher, which require specific baking treatments and process verification. Additionally, F1941 provides critical guidelines for maintaining thread fit, ensuring that coating thickness does not cause internal or external threads to transgress basic thread size limits.
Coating Properties
The following tables detail the material designations, thickness classes, and corrosion resistance benchmarks required under ASTM F1941. These properties are essential for selecting the appropriate finish based on environmental exposure and mechanical requirements.
| Coating Materials Designation | |
|---|---|
| Coating Designation | Coating Type |
| Fe/Zn | Zinc |
| Fe/Cd | Cadmium |
| Fe/Zn-Co | Zinc Cobalt Alloy |
| Fe/Zn-Ni | Zinc Nickel Alloy |
| Fe/Zn-Fe | Zinc Iron Alloy |
| Coating Thickness Designation | |
|---|---|
| Thickness Designation | Minimum Thickness (in.) |
| 3 | 0.0001 |
| 5 | 0.0002 |
| 8 | 0.0003 |
| 12 | 0.0005 |
| Chromate Finish Designation | ||
|---|---|---|
| Designation | Type | Typical Appearance |
| A | Clear | Transparent colorless with slight iridescence |
| B | Blue-bright | Transparent with a bluish tinge and slight iridescence |
| C | Yellow | Yellow iridescent |
| D | Opaque | Olive green, shading to brown or bronze |
| E | Black | Black with slight iridescence |
| F | Organic | Any of the above plus organic topcoat |
| Classification Code and Neutral Salt Spray Corrosion Protection Performance of Zinc and Cadmium Coatings | |||||
|---|---|---|---|---|---|
| Classification Code | Minimum Thickness (in.) | Chromate Finish Designation | First Appearance of White Corrosion (h) | First Appearance of Red Rust - Cadmium (h) | First Appearance of Red Rust - Zinc (h) |
| Fe/Zn or Fe/Cd 3A / 3B | 0.0001 | A, B, C, D | 6, 12, 24, 24 | 24, 36, 36, 36 | 12, 12, 24, 24 |
| Fe/Zn or Fe/Cd 3C / 3D | 0.0001 | C, D | 24, 24 | 36, 36 | 24, 24 |
| Fe/Zn or Fe/Cd 5A | 0.0002 | A | 6 | 48 | 24 |
| Fe/Zn or Fe/Cd 5B | 0.0002 | B | 12 | 72 | 36 |
| Fe/Zn or Fe/Cd 5C / 5D | 0.0002 | C, D | 48, 72 | 120, 168 | 72, 96 |
| Fe/Zn or Fe/Cd 5E | 0.0002 | E | 12 | 72 | 36 |
| Fe/Zn or Fe/Cd 8A / 8B | 0.0003 | A, B | 6, 24 | 96, 120 | 48, 72 |
| Fe/Zn or Fe/Cd 8C / 8D | 0.0003 | C, D | 72, 96 | 168, 192 | 120, 144 |
| Fe/Zn or Fe/Cd 8E | 0.0003 | E | 24 | 120 | 72 |
| Fe/Zn or Fe/Cd 12A / 12B | 0.0005 | A, B | 6, 24 | 144, 192 | 72, 96 |
| Fe/Zn or Fe/Cd 12C / 12D | 0.0005 | C, D | 72, 96 | 240, 264 | 144, 168 |
| Fe/Zn or Fe/Cd 12E | 0.0005 | E | 24 | 192 | 96 |
| Classification Code and Neutral Salt Spray Protection of Zinc Coatings with Non-Hexavalent Supplemental Passivate Finish | ||||
|---|---|---|---|---|
| Classification Code | Minimum Thickness (in.) | Chromate Finish Designation | First Appearance of Zinc Corrosion (h) | First Appearance of Red Rust (h) |
| Fe/Zn 5AS | 0.0002 | A | 96 | 120 |
| Fe/Zn 8AS | 0.0003 | A | 96 | 144 |
| Fe/Zn 12AS | 0.0005 | A | 96 | 168 |
| Classification Code and Neutral Salt Spray Corrosion Protection Performance of Zinc-Cobalt Coatings | ||||
|---|---|---|---|---|
| Classification Code | Minimum Thickness (in.) | Chromate Finish Designation | First Appearance of Alloy Corrosion (h) | First Appearance of Red Rust (h) |
| Fe/Zn-Co 5C / 5D | 0.0002 | C, D | 96 | 240 |
| Fe/Zn-Co 5F | 0.0002 | F | 196 | 340 |
| Fe/Zn-Co 8C / 8D | 0.0003 | C, D | 96 | 240 |
| Fe/Zn-Co 12C / 12D | 0.0005 | C, D | 96 | 400 |
| Classification Code and Neutral Salt Spray Corrosion Protection Performance of Zinc-Nickel Coatings | ||||
|---|---|---|---|---|
| Classification Code | Minimum Thickness (in.) | Chromate Finish Designation | First Appearance of Alloy Corrosion (h) | First Appearance of Red Rust (h) |
| Fe/Zn-Ni 5C / 5D | 0.0002 | C, D | 120, 180 | 500, 750 |
| Fe/Zn-Ni 8C / 8D | 0.0003 | C, D | 120, 180 | 720, 960 |
| Fe/Zn-Ni 12C / 12D | 0.0005 | C, D | 120, 180 | 960, 1000 |
| Fe/Zn-Ni 12D/F | 0.0005 | D/F | 300 | 1500 |
| Classification Code and Neutral Salt Spray Corrosion Protection Performance of Zinc-Iron Coatings | ||||
|---|---|---|---|---|
| Classification Code | Minimum Thickness (in.) | Chromate Finish Designation | First Appearance of Alloy Corrosion (h) | First Appearance of Red Rust (h) |
| Fe/Zn-Fe 5E | 0.0002 | E | 144 | 312 |
| Fe/Zn-Fe 8E | 0.0003 | E | 144 | 312 |
| Fe/Zn-Fe 12E | 0.0005 | E | 144 | 480 |