AMS 2471 — Anodizing of Titanium and Titanium Alloys
Engineering reference for SAE AMS 2471H, the primary aerospace specification for Type II sulfuric acid anodizing of titanium. Covers process chemistry, voltage ranges, color mapping, inspection, and certification.
TLDR
AMS 2471H is the SAE International specification governing Type II sulfuric acid anodizing of titanium and titanium alloys. It is the most widely cited aerospace anodizing standard for titanium — used wherever identification-marking color, paint adhesion, or enhanced corrosion resistance is required without compromising fatigue performance.
Quick Answer
What does AMS 2471 cover?
AMS 2471 defines the process parameters, bath chemistry, voltage ranges, color-to-voltage mapping, pre- and post-anodize cleaning, inspection criteria, and certification requirements for Type II (sulfuric acid) anodizing of titanium. It applies to wrought and cast products in grades 1–38 and is referenced by virtually every aerospace OEM for cosmetic, identification, and corrosion-protection anodizing of titanium components.
Scope
AMS 2471 applies to titanium and titanium alloy parts that require a uniform, controlled-thickness oxide layer produced by electrochemical treatment in a sulfuric-acid electrolyte.
Key parameters covered:
- Bath composition: 10–15 % sulfuric acid (H₂SO₄) by weight, balance deionized water
- Operating temperature: 21–32 °C (70–90 °F)
- Voltage range: 5–110 V DC (typically 18–22 V for identification colors)
- Current density: 1.0–2.5 A/dm² (10–25 A/ft²)
- Anodizing time: until voltage stabilizes (typically 5–15 min)
- Applicable alloys: all commercially pure and alloyed titanium grades (Grade 1 through Grade 38)
Process Steps
- Pre-cleaning. Degrease per ASTM D740, alkaline clean, and acid pickle (HF/HNO₃) to remove scale and embedded iron.
- Rinse. Deionized water rinse between every chemical step.
- Anodizing. Immerse parts as the anode in the sulfuric acid bath; ramp voltage to the target value at ≤ 5 V/s.
- Color stabilization. Hold at target voltage for 60–120 s to lock the interference color.
- Post-rinse and dry. Deionized water rinse, forced-air dry at ≤ 70 °C.
- Sealing (optional). Hot deionized water seal (≥ 90 °C, 15 min) for medical and chemical-service parts.
Voltage-to-Color Mapping
| Voltage (V) | Nominal Color | Typical Use |
|---|---|---|
| 10–15 | Gold / champagne | Decorative trim, premium consumer |
| 18–22 | Bronze / copper | Aerospace identification marking |
| 25–30 | Violet / purple | Medical implant color-coding |
| 33–38 | Royal blue | Medical, premium consumer |
| 45–55 | Sky blue | Decorative |
| 60–70 | Pale yellow | Aerospace fastener ID |
| 75–85 | Yellow / amber | Decorative |
| 90–100 | Magenta | Specialty identification |
| 110+ | Green / grey-green | Limited use |
Key Requirements
- Surface preparation. No embedded iron, no α-case > 0.0005 in, no residual lubricants.
- Color uniformity. ±5 V across the entire lot for matching color.
- Coating weight. Not specified by weight; thickness controlled by voltage and time (typically 0.02–0.5 µm oxide).
- Adhesion. Tape adhesion per ASTM D3359 after paint application.
- Corrosion performance. 168 h neutral salt spray (ASTM B117) without substrate attack.
- Hydrogen embrittlement. Vacuum-degas at 540–760 °C for ≥ 2 h after anodizing for fracture-critical parts (per AMS 2750).
Inspection and Certification
- Visual inspection. Color comparison against a reference coupon under D65 illumination.
- Coating thickness. Eddy-current or ellipsometry; typical range 0.02–0.5 µm.
- Adhesion testing. Tape test (ASTM D3359 Method B) for painted parts.
- MTR / CoC. Mill Test Report for substrate; Certificate of Conformance for anodize.
Typical Applications
- Aerospace: Identification marking on fasteners, brackets, hydraulic lines
- Medical: Color-coded implants, surgical instrument ID
- Defense: Optical components, weapon system identification
- Consumer: Premium watches, bicycle frames, jewelry
Related Materials
- Grade 2 Titanium — Standard substrate for anodized chemical-processing and medical parts
- Grade 5 Titanium (Ti-6Al-4V) — Aerospace workhorse; anodized for identification
- Grade 23 Titanium (Ti-6Al-4V ELI) — Medical implants; requires vacuum-degas post-anodize
Related Services
- Titanium Anodizing (Type II) — Production anodizing per AMS 2471H
- Titanium Anodizing (Type III / Hardcoat) — Wear-resistant anodizing per AMS 2488J
- Passivation — Pre-anodize cleaning per AMS 2700F
Related Standards
- AMS 2488J — Hard Anodizing of Titanium (Type III)
- AMS 2700F — Passivation of Corrosion-Resistant Steels and Titanium
- ASTM B862 — Titanium Welded Pipe (referenced for welded-and-anodized pipe)
- ASTM F86 — Surface Preparation of Surgical Implants