Chemical Conversion Coating of Aircraft Parts

Chemical conversion coating (CCC) is a surface treatment process used in the aerospace industry to enhance the corrosion resistance, adhesion properties, and overall durability of aircraft components. It involves chemically altering the surface of metal parts to form a protective oxide or phosphate layer.

Types of Chemical Conversion Coatings Used in Aerospace

1. Chromate Conversion Coating (Alodine or Iridite)

• Purpose: Provides corrosion resistance and improves paint adhesion.
• Materials: Typically applied to aluminum and aluminum alloys using hexavalent or trivalent chromium solutions.
• Application: Used on airframes, fuselage panels, and avionics enclosures.
• Standards: MIL-DTL-5541 (Class 1A for maximum corrosion resistance, Class 3 for electrical conductivity).

2. Phosphate Conversion Coating (Zinc or Manganese Phosphate)

• Purpose: Improves corrosion resistance and provides a surface for lubrication or paint adhesion.
• Materials: Applied to steel components using phosphoric acid-based solutions.
• Application: Used on landing gear components, fasteners, and hydraulic system parts.

3. Anodizing (Sulfuric or Hard Anodizing)

• Purpose: Forms an oxide layer on aluminum for enhanced corrosion and wear resistance.
• Materials: Uses sulfuric acid (Type II) or hard anodizing (Type III).
• Application: Applied to aircraft structural parts, engine components, and fuel system parts.

Application Process

1. Surface Cleaning – Parts are cleaned to remove grease, dirt, and oxidation.
2. Chemical Treatment – The metal surface is exposed to a chemical bath that forms a protective layer.
3. Rinsing and Drying – Excess chemicals are removed, and the coating is sealed or dried.
4. Post-Treatment (Optional) – Additional sealing or painting may be applied for enhanced protection.

Benefits of Chemical Conversion Coating

✔ Corrosion Resistance – Protects against oxidation and environmental degradation. ✔ Improved Paint Adhesion – Creates a strong base layer for coatings and primers. ✔ Electrical Conductivity (Class 3 Chromate Coatings) – Maintains conductivity in avionics components. ✔ Lightweight Protection – Does not add significant weight to aircraft structures. ✔ Extended Component Life – Reduces wear and tear on critical aerospace parts.