AMS 2700 — Passivation of Corrosion-Resistant Steels and Titanium Alloys
Engineering reference for SAE AMS 2700F, the corrosion-resistance passivation specification applied to titanium. Covers nitric and citric acid processes, pre-cleaning requirements, and acceptance criteria.
TLDR
AMS 2700F is the SAE International specification for chemical passivation of corrosion-resistant steels and titanium alloys. For titanium, it covers nitric acid and citric acid passivation — the two chemistries used to restore and stabilize the native TiO₂ oxide layer after machining, forming, or other surface-disturbing operations.
Quick Answer
What does AMS 2700 cover?
AMS 2700F defines the process parameters, bath chemistry, pre-cleaning, and acceptance criteria for passivating titanium and titanium alloy parts. Two chemistries are covered: nitric acid (HNO₃) passivation for general industrial and aerospace use, and citric acid passivation for medical, food-contact, and nuclear applications where nitric residue is restricted.
Scope
AMS 2700 is the master passivation specification covering austenitic, ferritic, martensitic, and precipitation-hardening stainless steels and titanium and titanium alloys. The titanium-specific provisions are covered in §3.4 and Annex A.
Key parameters (titanium section):
- Nitric acid process: 20–50 % HNO₃ by volume, 20–60 °C, 20–60 min immersion
- Citric acid process: 4–10 % citric acid by weight, 50–70 °C, 15–30 min immersion
- Pre-cleaning: mandatory alkaline clean + acid pickle (HF/HNO₃) to remove scale and embedded iron
- Final rinse: deionized water, ≤ 1 µS/cm conductivity
Process Steps
- Pre-clean. Degrease per ASTM D740, alkaline clean, and acid pickle to remove machining residue and embedded contaminants.
- Rinse. Deionized water rinse.
- Passivate. Immerse in nitric or citric acid bath per AMS 2700F § 3.4 time/temperature table.
- Rinse. Deionized water rinse until conductivity ≤ 1 µS/cm.
- Dry. Forced-air dry at ≤ 70 °C or vacuum dry.
Nitric vs. Citric Acid
| Parameter | Nitric Acid | Citric Acid |
|---|---|---|
| Typical concentration | 20–50 % | 4–10 % |
| Operating temperature | 20–60 °C | 50–70 °C |
| Immersion time | 20–60 min | 15–30 min |
| Oxide thickness added | minimal (stabilization) | minimal (stabilization) |
| Medical / food use | Limited (nitrate residue) | Preferred |
| Aerospace use | Standard | Growing |
| Cost | Lower | Slightly higher |
The choice between nitric and citric is typically driven by end-use regulatory restrictions: medical and food-contact parts almost universally specify citric acid to avoid nitrate residue.
Key Requirements
- No embedded iron. Pre-passivation cleaning per ASTM A967 § 6 is mandatory. Iron contamination causes post-passivation rust spots that fail acceptance.
- Dissolved-oxygen stability. Citric acid passivation requires dissolved oxygen ≥ 4 ppm; aerate the bath or use cascade aeration.
- No bleached-out or stained surface. Acceptable: uniform color shift consistent with alloy. Unacceptable: rainbow staining, white powder, etch pitting.
- Surface resistivity. Optional per OEM; typical medical spec ≥ 30 MΩ at 100 V.
- Documentation. CoC per lot; MTR for substrate chemistry.
Common Pitfalls
- Insufficient pre-cleaning. Embedded iron or carbon-steel particles from machining cannot be removed by passivation; they will rust through the new oxide within days.
- Bath age. Nitric acid passivation baths accumulate dissolved titanium and lose activity; replace per OEM schedule (typically every 50–100 cycles).
- Agitation. Stagnant baths produce non-uniform passivation; use mechanical agitation or recirculation per AMS 2700F § 3.5.
Typical Applications
- Aerospace: Hydraulic fittings, structural machined components
- Medical: Implants, surgical instruments, dental components (citric acid)
- Chemical processing: Reactor internals, valve bodies
- Marine: Seawater-system components
- Food processing: Conveyors, mixing equipment (citric acid)
Related Materials
- Grade 2 Titanium — Most common passivated substrate
- Grade 5 Titanium (Ti-6Al-4V) — Aerospace structural components
- Grade 23 Titanium (Ti-6Al-4V ELI) — Medical implants (citric acid preferred)
Related Standards
- ASTM A967 / A967M — Chemical passivation treatments for stainless parts (widely applied to titanium by extension)
- ASTM F86 — Surface preparation of surgical implants (uses AMS 2700 as a baseline)
- AMS 2471H — Type II anodizing (uses passivation as pre-treatment)
- ASTM B912 — Electropolishing as a passivation method