1. Why Surface Treatment is Needed
Surface treatment is a critical post-processing step in precision parts manufacturing, primarily for:
- Corrosion resistance: Protect metal substrate from oxidation, acids, alkalis, seawater
- Wear resistance: Increase surface hardness, reduce friction and wear
- Decoration: Achieve various colors, gloss levels, textures
- Electrical properties: Improve conductivity or achieve electrical insulation
- Hide machining marks: Cover tool marks, scratches, color differences for uniform surface
- Coating adhesion: As pretreatment for painting and powder coating
2. Anodizing
Principle
Anodizing uses aluminum, magnesium, titanium or other reactive metals as the anode in an electrolyte solution with electric current, generating a dense oxide film on the metal surface. Aluminum alloy anodizing is the most common.
Common Types
| Type | Coating Thickness | Hardness | Features |
|---|---|---|---|
| Standard anodizing (sulfuric acid) | 5~15μm | HV200~300 | Low cost, rich colors, good corrosion resistance |
| Hard anodizing | 25~100μm | HV400~600 | Thick film, high hardness, wear/insulation resistant, for harsh environments |
| Chromic acid anodizing | 2~5μm | Lower | Thin film, does not affect fatigue strength, for aerospace parts |
| Chemical oxidation (conductive) | 0.5~2μm | Low | Thin film, conductive, low cost, as painting base |
Color Options
Anodized film has a porous structure that can absorb dyes for various colors: natural (silver white), black (most common), red, blue, green, gold, gray, champagne, etc.
Suitable Materials
Mainly aluminum alloys (6061, 7075, 5052, etc.). 6061 gives the best and most uniform results; 7075 oxidizes darker due to high copper content; 5052 gives a bluish-white softer film; 2024 has poor anodizing results with potential color differences.