Anodizing, an electrochemical process used to alter metal surfaces, is a core technology in aerospace and industrial manufacturing. It improves corrosion resistance and changes appearance by forming an oxide layer that is tightly bonded to the base metal. The layer is part of the substrate rather than an applied coating, so it does not peel.
Anodizing is a controlled oxidation process. Aluminum alloy or other metal components are immersed in an electrolyte and connected as the anode; when current is applied, a dense oxide film forms on the surface.
The film offers high hardness, electrical insulation and corrosion protection. Because it grows from the metal itself, it resists flaking and peeling in ways that conventional coatings do not.
Aluminum surface treatments are selected according to application requirements, and each process gives the metal different properties.
| Process | Key characteristics |
|---|---|
| Hard anodizing | High wear resistance and hardness; suited to heavily loaded components. |
| Sulfuric acid anodizing | Most common industrial treatment; uniform film and easy to dye. |
| Chromic acid anodizing | Excellent corrosion resistance; often used for aerospace structural parts. |
| Chemical conversion coating | Provides conductivity and coating adhesion; often used as a pretreatment. |
| Black oxide | Produces a matte black finish; rust resistance is enhanced when combined with oil impregnation. |
Since 1960, metal surface treatment has been indispensable to the aerospace industry. Aircraft parts face strict requirements for dimensional stability and fatigue resistance, and surface-treatment suppliers must pass rigorous qualification.
NADCAP accreditation and supplier approval from major airframe manufacturers such as Boeing are key measures of a company's technical capability in this field.
- Electroplating: nickel, zinc-nickel, copper, chromium, silver, gold, cadmium and tin, used to improve conductivity or solderability.
- Conversion coatings: passivating and phosphating, mainly used to improve the corrosion-resistant base of metals.
- Special functional coatings: dry-film lubrication and vacuum impregnation, used to address mechanical friction and sealing problems in specific environments.
These processes are selected for specific functions, including electrical conductivity, solderability, friction control and sealing in demanding environments.
