What is BSAA (Boric-Sulfuric Acid Anodize)?

BSAA (Boric-Sulfuric Acid Anodize) is an environmentally-friendly anodizing process developed by Boeing in 1990 that provides equivalent corrosion resistance to chromic acid anodize (Type I) while eliminating hexavalent chromium. When combined with trivalent chromium seals like Metalast TCP-HF, BSAA achieves full RoHS, REACH, and WEEE compliance.

Is BSAA approved by Sikorsky, Bell Helicopter, and Airbus?

Yes. Anoplate is officially Sikorsky approved for Type IC (BSAA) processing with advanced trivalent chromium sealing technology (Metalast TCP-HF). Bell Helicopter approves BSAA for adhesive bonding applications, and Airbus has approved BSAA for aerospace manufacturing. Anoplate is AS9100 certified.

How does BSAA compare to chromic acid anodize?

BSAA exceeds the industry standard 336-hour salt spray test requirement and outperforms chromic acid anodize in corrosion resistance. Both Type I chromic anodize and BSAA exhibit approximately 5% fatigue strength reduction, making them ideal for high-stress aerospace applications.

What is a trivalent chromium seal?

A trivalent chromium seal (Cr III) such as Metalast TCP-HF replaces traditional hexavalent chromium (Cr VI or chromates) used in anodizing. Trivalent seals eliminate toxic hexavalent chromium while maintaining 336-hour salt spray corrosion resistance. Sikorsky now mandates trivalent chromium seals for all BSAA Type IC processing.

What are the fatigue strength impacts of different anodizing types?

Type I (Chromic & BSAA): ~5% fatigue reduction - ideal for high-stress aerospace. Type II (Sulfuric): ~25% fatigue reduction - moderate protection. Type III (Hardcoat): up to 50% fatigue reduction - maximum wear resistance but lowest fatigue strength.

Is BSAA RoHS, REACH, and WEEE compliant?

Yes. BSAA with trivalent chromium seals (such as Metalast TCP-HF) is fully compliant with RoHS (Restriction of Hazardous Substances), REACH (Registration, Evaluation, Authorization and Restriction of Chemicals), and WEEE (Waste Electrical and Electronic Equipment) directives.

What is the 336-hour salt spray test?

The 336-hour salt spray test (ASTM B117) is the aerospace industry standard for measuring anodizing film corrosion resistance. Both BSAA and chromic acid anodize must meet and exceed this threshold. BSAA exceeds industry standards.

When should I NOT use BSAA?

Avoid BSAA for: (1) Parts requiring both hardcoat anodize (Type III) and chromic anodize on the same component; (2) Components with welds, crimps, or seams where sulfuric acid might be trapped; (3) Applications requiring dyed black finishes. For dyed applications, use Type I chromic anodize or Type II sulfuric anodize.

What adhesive bonding alternatives exist?

Sikorsky and Bell Helicopter prefer phosphoric acid anodize for maximum adhesive bonding strength; Airbus favors tartaric acid anodize. However, BSAA remains the only alternative that exceeds chromic acid anodize's corrosion performance while providing adequate adhesive bonding.

Boric Sulfuric Acid Anodize (BSAA)

Name: Anoplate
Rating: 4.9

by Erisson Lima

Chromic acid anodize (also known as Type I anodize per MIL-DTL-8625) has traditionally been used in the following aerospace anodizing applications:

Airframe components due to its increased corrosion resistance and fatigue strength retention
Tight-tolerance aluminum parts requiring corrosion protection and aerospace sealing
Aluminum components adhesively bonded to one another for aircraft structures
Military aircraft coatings and defense applications
Helicopter rotor components and structural elements

These attributes have been ideal for aircraft coatings, metal finishing aerospace, and aluminum anodizing for aviation. As its name denotes, chromic acid anodize is an aluminum oxide coating created in a chromic acid solution.

Regulatory Compliance & Environmental Standards

EH&S and EU legislations (including RoHS compliance, REACH regulations, and WEEE directives) have called for the ban of hexavalent chromium (a.k.a. chromates and dichromate seals) not only in coatings but also in the manufacturing process and metal finishing industry. In response to this regulatory trend in aerospace manufacturing, in 1990 Boeing developed and patented Boric Sulfuric Acid Anodize (BSAA).

BSAA vs CAA - Comparison Table & Alternatives to Chromic Acid Anodize

Boeing initially licensed the patented process to qualified vendors; however, that patent has since expired. The BSAA oxide coating exhibits many of the same properties as the aluminum oxide coating derived from the chromic acid process. Boric-Sulfuric Acid Anodize is now the leading environmentally-friendly anodize alternative to CAA.

Other Chromic Anodize Alternatives:

Phosphoric acid anodize (for adhesive bonding)
Tartaric acid anodize (for aircraft bonding applications)
Trivalent chromium seal (Cr III replacement for hexavalent chromium)
Metalast TCP-HF seal

Design Considerations with BSAA - When to Use BSAA vs CAA

In considering whether BSAA would be a functional alternative to the chromic acid anodize you've been specifying for years, there is very little to consider. If your parts require hardcoat anodize (Type III) and chromic anodize on the same part, and your metal finisher has been using chromic acid anodize as a stop-off layer, BSAA will not be for you.

Also, because the electrolyte used for developing this coating contains sulfuric acid, there is a chance to entrap solution in welds, crimps, and seams, which can lead to corrosion and part degradation. Parts with these features would not be good candidates for BSAA.

Furthermore, while modifying electrolyte conditions for chromic anodize allows those anodic oxide films to be dyed (black, in particular), BSAA doesn't permit such a dyed opportunity. While these design considerations have been investigated, there are many more attributes that one might specify CAA for and reasons why it has worked in your aerospace application and military specifications.

Aerospace Primes Approving BSAA - Sikorsky, Bell, Airbus

Prime Specifications Aerospace such as Sikorsky, Bell Helicopter, and Airbus have been permitting the switch to BSAA where Type I chromic anodize was specified for years.

Sikorsky has taken BSAA to the next level of environmental impact by specifying the use of a trivalent chromium seal (e.g. Metalast TCP-HF) over the traditional dilute dichromate seal, eliminating hexavalent chromium entirely from the anodizing process.

Anoplate is proud to announce we are Sikorsky approved for Type IC (BSAA) processing with advanced sealing technology.

BSAA Benefits: Fatigue Strength & Corrosion Protection

One of the largest benefits of thin anodic films used in the aerospace industry – be it chromic anodize or boric-sulfuric anodize – is their ability to provide corrosion protection without greatly diminishing the fatigue strength of the aluminum base material.

Type I (CAA & BSAA): ~5% or less fatigue reduction
Type II (Sulfuric Anodize): ~25% fatigue reduction
Type III (Hardcoat Anodize): up to 50% fatigue reduction

BSAA exceeds standard corrosion performance and meets the industry standard 336 hour salt spray test for anodizing films.

Adhesive Bonding Applications - BSAA vs Phosphoric vs Tartaric Anodize

While BSAA is suitable as a primer for adhesive bonding, many aerospace primes are looking to chromic anodize alternatives for even greater bonding strength. Sikorsky and Bell Helicopter favor phosphoric acid anodize as optimum for adhesive bonding applications, whereas Airbus is turning towards tartaric acid anodize.

Why Switch from CAA to BSAA Today

✈️ Environmentally-responsible replacement to chromic acid anodize
✈️ RoHS, REACH, WEEE compliant
✈️ Hexavalent chromium-free manufacturing
✈️ Maintains fatigue strength of aluminum
✈️ Superior corrosion resistance (336-hour salt spray)
✈️ Aerospace prime approved (Sikorsky, Bell, Airbus)

Boric-Sulfuric Acid Anodize represents a leap forward in providing an environmentally-responsible replacement to chromic acid anodize for straightforward corrosion resistance applications in aerospace manufacturing.