The Ti-6Al-4V alpha-beta alloy is the most widely utilized titanium grade in the world. When manufactured for high-critical aerospace applications, it must conform to strict industry standards. The premier standard governing this material is AMS 4911 (Titanium Alloy, Sheet, Strip, and Plate, 6Al – 4V, Annealed).
This comprehensive guide breaks down the technical requirements of the latest AMS 4911S (Revised August 2024) specification, helping engineers, procurement managers, and quality control teams ensure full compliance.
1. Scope and Application of AMS 4911
The AMS 4911 specification covers the Ti-6Al-4V grade in the form of sheet, strip, and plate up through 4.000 inches (101.60 mm) inclusive in nominal thickness.
- Typical Application: These aerospace-grade products are typically used for structural parts requiring reliable strength up to 750 °F (399 °C).
- Condition: The material must be supplied in the annealed condition, descaled, and leveled/flattened to commercial standards.
2. AMS 4911 Chemical Composition Limits (By Weight %)
To be certified as authentic AMS 4911S material, the chemical breakdown of the Ti-6Al-4V grade must strictly conform to the following weight percentages:
| Element | Minimum (%) | Maximum (%) |
| Aluminum (Al) | 5.50 | 6.75 |
| Vanadium (V) | 3.50 | 4.50 |
| Iron (Fe) | — | 0.30 |
| Oxygen (O) | — | 0.20 |
| Carbon (C) | — | 0.08 |
| Nitrogen (N) | — | 0.05 (500 ppm) |
| Hydrogen (H) | — | 0.015 (150 ppm) |
| Yttrium (Y) | — | 0.005 (50 ppm) |
| Other Elements, each | — | 0.10 |
| Other Elements, total | — | 0.40 |
| Titanium (Ti) | Remainder | Remainder |
3. Mechanical and Tensile Properties
Tensile property requirements apply to both the longitudinal and long transverse directions. The material must meet the following minimum thresholds after the specified annealing process:
Minimum Tensile Properties (Inch/Pound Units)
| Nominal Thickness (Inches) | Tensile Strength (ksi) | Yield Strength at 0.2% Offset (ksi) | Elongation in 2 Inches (%) |
| Up to 0.008, excl. | 134 | 126 | — |
| 0.008 to 0.025, excl. | 134 | 126 | 6 |
| 0.025 to 0.063, excl. | 134 | 126 | 8 |
| 0.063 to 0.1875, excl. | 134 | 126 | 10 |
| 0.1875 to 4.000, incl. | 130 | 120 | 10 |
4. Quality & Testing Requirements
- Melting Practice: The alloy must be multiple melted. The final melt cycle must utilize Vacuum Arc Remelting (VAR) to prevent alpha inclusions and impurities.
- Ultrasonic Inspection: Plates with a nominal thickness of 0.500 inch (12.70 mm) and over must undergo ultrasonic testing per AMS 2631 and meet Class A1 requirements.
- Surface Contamination: The product must be completely free of any oxygen-rich brittle layers, such as Alpha Case, verified via metallographic examination or microindentation hardness testing (ASTM E384).
5. Frequently Asked Questions (FAQ)
Q: What is the difference between AMS 4911R and AMS 4911S? A: AMS 4911S is the latest 2024 revision resulting from a 5-year review. It tightens definitions to explicitly prohibit unauthorized exceptions, relocates definitions, and updates referenced applicable documents.
Q: Can titanium bar stock be substituted for AMS 4911 plate? A: No. According to Section 3.3.2 of the specification, bar, billet, forgings, or forging stock shall not be substituted for plate products.
Q: What commercial finish is comparable to the AMS 4911 surface? A: Sheet and strip product finishes are comparable to a commercial corrosion-resistant steel No. 2D finish, while plates are comparable to a No. 1 finish.