ASTM F1136 – Coating Properties & Specification
ASTM F1136/F1136M is the industry standard for Zinc/Aluminum Corrosion Protective Coatings applied to fasteners. These inorganic basecoats are designed to provide high-performance corrosion resistance through a non-electrolytic process, typically involving dip-spin, dip-drain, or spray methods followed by a baking cycle (up to 330°C). For project application, this specification is categorized into six distinct grades, ranging from basic basecoats to advanced systems featuring clear, lubricated, or pigmented topcoats. It is a critical standard for preventing hydrogen embrittlement, as the coating process avoids the acid pickling or phosphating stages typically associated with traditional plating. When ordering, specifiers must define the Grade (1–6) and whether the coating should contain chrome (C) or be non-chrome (NC).
Coating Properties
The performance of an ASTM F1136 coating is defined by its thickness, weight, and Salt Spray Test (SST) endurance. As shown in the table below, higher grades generally offer increased protection. Grade 3 and 5, for instance, utilize sealers to achieve a minimum of 1000 hours of corrosion resistance in chrome-based systems. Technical requirements for successful application include an adhesion loss of less than 5% (via tape test per ASTM D3359) and a uniform appearance free from tears or blisters. For threaded parts, the coating thickness is carefully regulated to ensure it does not interfere with the GO thread gage fit, though some oversizing of internal threads may be required for heavier grades.
| Grade No. | Topcoat Type | Coating Thickness | Coating Weight | Minimum SST Hours (h) | |||
|---|---|---|---|---|---|---|---|
| Metric Average (μm) | Inch Average (mil) | Metric Average (g/m²) | Inch Average (oz/ft²) | (C) | (NC) | ||
| 1 | None | 4 to 5 | 0.16 to 0.20 | 16 to 20 | 0.052 to 0.066 | 240 | ---- |
| 2 | None | 5 to 8 | 0.20 to 0.31 | 20 to 28 | 0.066 to 0.092 | 500 | 240 |
| 3 | Clear Sealer | 6 to 12 | 0.24 to 0.47 | 22 to 34 | 0.072 to 0.111 | 1000 | 720 |
| 4 | None | 8 to 15 | 0.31 to 0.59 | 28 to 50 | 0.092 to 0.164 | 1000 | 500 |
| 5 | Lubricated Sealer | 6 to 12 | 0.24 to 0.47 | 22 to 34 | 0.072 to 0.111 | 1000 | 720 |
| 6 | Pigmented Topcoat | 8 to 15 | 0.31 to 0.59 | 23 to 40 | 0.075 to 0.131 | 500 | 500 |