Phosphating
Phosphating of Aircraft Parts
Phosphating is a chemical conversion coating process applied to steel and aluminum aircraft components to enhance corrosion resistance, improve paint adhesion, and reduce friction and wear. It involves treating the metal surface with a phosphoric acid-based solution, which reacts with the metal to form a thin, crystalline phosphate coating.
This process is widely used in landing gear, fasteners, hydraulic components, and aircraft structural elements to ensure longevity and performance under extreme conditions.
How Phosphating Works
- Surface Cleaning & Preparation Parts are cleaned and degreased to remove contaminants, oil, and oxidation. Acid pickling or blasting may be used to enhance adhesion.
- Chemical Phosphating Process The part is immersed in a phosphoric acid solution containing metal phosphates. A chemical reaction occurs, forming a crystalline phosphate layer on the metal surface.
- Post-Treatment (Optional) The coated part may be treated with sealers, oil, or paint for added corrosion protection and lubrication. The part is dried and cured to ensure durability.
Types of Phosphate Coatings Used in Aerospace
Benefits of Phosphating for Aircraft Parts
✅ Improves Corrosion Resistance – Acts as a barrier against oxidation and moisture. ✅ Enhances Paint & Primer Adhesion – Ensures a strong bond for topcoats. ✅ Reduces Friction & Wear – Manganese phosphate is ideal for moving parts like gears and bearings. ✅ Prevents Galling & Seizing – Important for fasteners and threaded components. ✅ Cost-Effective & Lightweight – Provides excellent protection without adding significant weight.
Aerospace Applications of Phosphating
✔ Landing Gear Components – Zinc phosphate coatings protect against corrosion and wear. ✔ Fasteners & Bolts – Enhances paint adhesion and prevents rust in high-stress environments. ✔ Hydraulic System Parts – Improves lubrication and wear resistance. ✔ Aircraft Fuel System Components – Protects against fuel and chemical exposure. ✔ Gears & Bearings – Manganese phosphate coatings reduce friction for smoother operation.
Comparison: Phosphating vs. Other Protective Coatings
| Type | Key Benefits | Typical Applications |
|---|---|---|
| Zinc Phosphate | Best corrosion resistance, excellent paint adhesion | Landing gear, aircraft fasteners, fuel system parts |
| Manganese Phosphate | Superior wear resistance, reduces friction | Engine components, bearings, gears |
| Iron Phosphate | Lightweight, good base for painting | Structural aircraft parts |
Challenges & Considerations
✖ Limited to Certain Metals – Mostly effective for steel and aluminum, not for titanium. ✖ Environmental Concerns – Some phosphate solutions contain hazardous chemicals. ✖ Additional Coatings May Be Needed – For extreme environments, phosphate coatings are often sealed with oil, paint, or epoxy for added durability.
Industry Standards & Compliance
- AMS 2481 – Aerospace standard for zinc phosphate coatings.
- MIL-DTL-16232 – Military specification for manganese phosphate coatings.
- ASTM D766 – Standard for iron phosphate coatings.
| Process | Corrosion Resistance | Wear Resistance | Adhesion Properties | Common Materials |
|---|---|---|---|---|
| Phosphating | Moderate-High | High (Manganese Type) | Excellent | Steel, Aluminum |
| Anodizing | Very High | Moderate | Good | Aluminum, Titanium |
| Chromate Conversion | Moderate | Low | Good | Aluminum |
| Electroless Nickel | Very High | High | Excellent | Steel, Aluminum |
| Zinc-Nickel Plating | Very High | Moderate | Good | Steel |
Parts that require Phosphating
| Part Number | Name | Alt Part Number | ATA Chapter | Cage Code | NSN | Rotable | Repair Stations | Suppliers |
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