I. Traditional surface treatment technology
1. Anodizing
- Principle: Generate a dense aluminum oxide layer (thickness 5-25μm) on the aluminum surface through electrolysis, with a hardness of up to HV300-500.
- Advantages: The salt spray test can reach more than 1000 hours, suitable for industrial scenes such as building curtain walls and ship accessories.
- Improvement direction: Sealing treatment (such as boiling water/nickel salt sealing) can increase porosity and reduce the risk of corrosive medium penetration.
2. Chemical conversion film
- Chromate treatment: Generate Cr(OH)3/CrO3 composite film with excellent corrosion resistance (salt spray test 500-800 hours), but there is a hexavalent chromium pollution problem.
- Environmentally friendly alternative: Chromium-free zirconium-titanium conversion solution (such as Henkel X4301), salt spray resistance of 300-500 hours, in line with RoHS standards.
2. Coating protection technology
1. Powder spraying
- Process: Electrostatic spraying of epoxy/polyester powder, forming a 60-120μm coating after curing at 200℃.
- Performance: Weather resistance 10-15 years (QUV aging test 2000 hours), suitable for outdoor advertising boards and containers.
2. Electrophoretic coating
- Features: Forming a uniform coating (15-30μm) through electrodeposition, which can cover the inner cavity of complex workpieces and resist salt spray ≥800 hours.
- Case: Automobile aluminum alloy wheels are mostly protected by cathode electrophoresis + transparent powder.
3. Advanced composite processing technology
1. Micro-arc oxidation (MAO)
- Technical parameters: Generate a ceramic oxide layer (50-200μm) under high voltage electric field, hardness HV800-1500, and neutral salt spray resistance ≥3000 hours.
- Application areas: Aerospace fasteners, offshore platform structural parts.
2. Laser cladding
- Process: Use laser to clad the Ni-based alloy layer on the aluminum surface to achieve metallurgical bonding, and improve corrosion resistance by 3-5 times.
- Cost: about ￥120-200/m², suitable for high-value components such as nuclear power equipment.
IV. Technical selection recommendations
| Demand scenarios | Recommended solutions | Cost (yuan/m²) | Salt spray resistance (hours) |
| Building exterior walls/outdoor signs | Anodic oxidation + fluorocarbon spraying | 80-150 | 1500+ |
| Auto parts | Chromium-free conversion film + cathode electrophoresis | 50-90 | 800-1200 |
| Marine engineering equipment | Micro-arc oxidation + silicone sealant | 200-300 | 3000+ |
| Food machinery (high environmental protection requirements) | Silanization treatment + epoxy powder | 70-110 | 600-800 |
V. Key steps for pretreatment
1. Degreasing and cleaning: Alkaline cleaning agent (pH 9-11) to remove oil stains and ensure that the surface tension is ≤35mN/m.
2. Pickling activation: Use nitric acid-hydrofluoric acid mixture (concentration 10%-15%) to remove the oxide scale, and the activation time is controlled within 2-5 minutes.
3. Water washing control: conductivity ≤50μS/cm to prevent residual impurity ions from affecting the adhesion of the coating.
> Note: The data refers to the test results of ASTM B117, ISO 9227 and other standards. The actual performance is affected by the base alloy model (such as 6061 vs 5052) and process parameters. It is recommended to conduct a small sample test (such as a 5cm×5cm test piece) before batch application.