Scope of AMS 4944 Tubing
AMS 4944 is the aerospace material specification for seamless tubing in the Ti-3Al-2.5V alloy, which carries UNS R56320 and the common designation Grade 9. The alloy was developed specifically for cold workable tubing: it is classified as a lean alpha-beta material, but its low alloy content means it retains many of the forming characteristics of commercially pure titanium while delivering substantially higher strength. Tubing made to this specification is used for hydraulic pressure and return lines, fuel lines and instrumentation on airframes and engines.
Mechanical Properties and Physical Data
In the annealed condition the alloy must reach a minimum tensile strength of 620 MPa (90 ksi), a minimum 0.2% offset yield strength of 483 MPa (70 ksi) and a minimum elongation of 15 percent in 50 mm. Typical production values run slightly higher, in the range of 620 to 654 MPa tensile and 483 to 503 MPa yield, with elongation between 20 and 27 percent, which gives a useful margin over the specification minimum and better fatigue performance for the same wall. Density is 4.48 g/cm3, the modulus of elasticity is about 105 GPa and the maximum recommended continuous operating temperature is approximately 315 C.
| Property | Typical Value | AMS 4944 / ASTM B338 Minimum |
|---|---|---|
| Tensile strength | 620-654 MPa | 620 MPa |
| Yield strength, 0.2% offset | 483-503 MPa | 483 MPa |
| Elongation in 50 mm | 20-27% | 15% |
| Modulus of elasticity | approx. 105 GPa | - |
| Density | 4.48 g/cm3 | - |
Why Hydraulic Systems Use Grade 9
Hydraulic lines on aircraft are pressure vessels that must be as light as possible and must survive vibration and pressure cycling without cracking. Grade 9 tubing satisfies both demands: the strength permits a thin wall, the ductility allows tight bends and flaring without annealing between operations, and the fatigue resistance at bend locations is better than that of the pure grades.
Hydraulic pressure, return and suction lines in airframes and engines.
Fuel and lubrication lines, including vent and drain runs.
Pneumatic and inert gas distribution tubing.
Space frame and lightweight structural tube where stiffness is not the governing factor.
Marine and offshore hydraulic control lines, where salt spray exposure is continuous.
Cold Drawing, Annealing and Forming
Tubing is produced by cold drawing over a mandrel or by cold pilgering, with intermediate annealing to restore ductility. Final annealing is carried out in a vacuum or high purity atmosphere furnace at around 700 to 790 C, and the finished tube is bright annealed or pickled to remove any oxygen enriched surface layer. Bending is performed on numerically controlled draw benders with a mandrel inside the tube to prevent wall thinning at the bend, and bend radii are normally kept at three times the outside diameter or greater. Flaring and beading operations are controlled by tooling with a soft contact face, because titanium galls against hardened steel and any surface tear becomes a fatigue crack origin. All forming is done on dedicated equipment that has not been used on carbon steel, so that iron contamination cannot be transferred.
Welding, Testing and Certification
Joints are made by TIG or orbital welding under a full internal argon purge and a trailing shield, with shielding maintained until the joint cools below about 400 C. Shielding quality is verified by the colour of the finished weld, and welds are then radiographed or dye penetrant inspected according to the engineering drawing. Tube is delivered with full length eddy current examination, a flattening test and a hydraulic proof pressure test. Surface condition is bright annealed or pickled, with caps on both ends to preserve bore cleanliness. Documentation includes an EN 10204 3.1 mill test certificate with heat number traceability, dimensional records and non destructive test reports, and qualification data can be supplied against the customer's own specification for programme approval. Tube is packed in rigid crates or on lined reels so that it arrives straight and free of handling marks.
Frequently Asked Questions
Q: What does AMS 4944 cover?
A: It covers seamless tubing in the Ti-3Al-2.5V alloy for hydraulic and similar fluid systems, with the property requirements and testing listed for the annealed condition.
Q: Can Grade 9 tubing be strengthened by heat treatment?
A: Not meaningfully. Aging produces no useful increase in strength, so design values are taken from the annealed condition at 620 MPa minimum tensile strength.
Q: How does it compare with commercially pure titanium tubing?
A: Its room temperature and elevated temperature strength is 20 to 50 percent higher than pure titanium, while weldability and cold forming behaviour remain excellent.
Q: What wall thicknesses are available?
A: Standard hydraulic sizes run from about 6 mm to 25 mm outside diameter with wall thickness from 0.5 mm to 2 mm, and other combinations are produced to order.
Q: How is bore cleanliness controlled?
A: After final annealing and testing the bore is flushed, dried and capped. Particle counts can be verified on request for hydraulic circuits with strict cleanliness classes.
