BSA - Boric-Sulfuric Acid Anodizing
Overview of BSA (Boric-Sulfuric Acid Anodizing)
BSA (Boric-Sulfuric Acid Anodizing) is an environmentally friendlier alternative to traditional Type I Chromic Acid Anodizing. It is widely used in the aerospace and defense industries for corrosion protection, paint adhesion, and fatigue resistance. BSA offers similar protective properties to chromic acid anodizing but eliminates the use of hexavalent chromium, making it compliant with modern RoHS, REACH, and environmental directives. It is particularly well-suited for structural aluminum components and assemblies requiring bonding.
Key Benefits of BSA:
- Non-chromated, environmentally compliant alternative to Type I anodizing
- Excellent corrosion resistance and paint adhesion
- Minimal dimensional change—ideal for tight tolerance parts
- Preserves fatigue strength of aluminum components
- Approved by major aerospace OEMs and compliant with MIL-DTL-8625 Type IC
Boric-Sulfuric Anodizing Process
BSA uses a mixture of boric acid and sulfuric acid as the electrolyte. The anodizing process is performed at low temperatures and controlled current densities to produce a thin, uniform oxide layer typically around 0.00002" to 0.0001" thick. The resulting finish is similar in function to chromic acid anodizing but more environmentally responsible.
1. Surface Preparation
The part is cleaned, degreased, and deoxidized to remove surface contaminants and promote uniform anodic film formation.
2. Anodizing
The part is connected as the anode and immersed in a bath of boric-sulfuric acid solution, typically at 20-25°C (68-77°F). The process uses a controlled current density (around 4.5-6 A/ft²) to grow the oxide layer slowly and evenly.
3. Rinsing and Sealing
After anodizing, the part is rinsed and sealed in hot deionized water or a sealing solution. Sealing enhances corrosion resistance and closes the porous structure of the oxide layer.
Compatible Substrates for BSA
BSA is compatible with most aerospace-grade aluminum alloys, including:
- 2000 series: Requires special care due to copper content
- 5000, 6000, and 7000 series: Commonly anodized using BSA
- 2024, 6061, 7075: Typical aerospace alloys used in airframes and structures
Applications of Boric-Sulfuric Acid Anodizing
- Aerospace: Skins, panels, structural frames, and bonded assemblies
- Defense: Precision machined components and corrosion-resistant hardware
- Electronics: Housings and conductive surfaces requiring adhesive bonding
- Industrial: Non-decorative aluminum parts needing corrosion protection and minimal oxide buildup
Environmental and Regulatory Considerations
BSA is a hexavalent chromium-free process that supports global initiatives to reduce hazardous waste and eliminate carcinogenic substances in manufacturing. It meets compliance standards under REACH, RoHS, ELV, and is increasingly specified by OEMs seeking safer anodizing solutions.
Conclusion
Boric-Sulfuric Acid Anodizing offers aerospace-grade corrosion protection and paint bonding performance without the environmental and health concerns of chromic acid anodizing. As a proven and qualified alternative under MIL-DTL-8625 Type IC, BSA continues to gain adoption in industries requiring high-performance coatings and regulatory compliance.
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