AMS 6390
AMS 6390 is the SAE Aerospace Material Specification for SAE 4140 chromium-molybdenum alloy steel seamless tubing. The specification covers tubing produced by hot or cold working in outside diameters from 0.500 inch to 8.000 inches with wall thicknesses from 0.049 inch to 1.000 inch, in the annealed, normalized, or quenched and tempered condition. Chemical composition, dimensional tolerances, mechanical properties, and non-destructive inspection requirements are specified for aerospace-quality seamless 4140 tubing.
AMS 6390 tubing is the primary specification for hydraulic cylinder barrels, actuator bodies, and high-pressure aerospace accumulator shells in applications requiring greater strength than AMS 6346 (4130) tubing can provide. Its through-hardened capability to 200 ksi in moderate wall thicknesses makes it the standard material for aerospace hydraulic cylinders on commercial and military aircraft landing gear and flight control actuator systems.
AMS 6390 tubing in the Q&T condition to 180,000 psi develops minimum 180,000 psi UTS, 163,000 psi yield strength, 10% elongation, and 40% reduction of area. Hydrostatic testing and eddy current or ultrasonic inspection are performed at the mill per AMS 6390 requirements. The seamless manufacturing process ensures uniform wall thickness and freedom from longitudinal weld discontinuities, both critical for high-pressure hydraulic cylinder service where weld seams can be fatigue crack initiation sites.
- Aircraft landing gear hydraulic actuator cylinders
- Flight control actuator body tubes
- High-pressure aerospace accumulators and reservoirs
- Helicopter rotor servo actuator cylinders
- Aerospace brake actuator and steering cylinder bodies
Certified Material for Critical Service
AMS 6390 tubing certifications include chemical composition, mechanical properties (in the applicable heat treat condition), dimensional inspection results, and hydrostatic or non-destructive inspection records. Full traceability by heat and lot number is maintained. For hydraulic system applications, tubing must additionally comply with the applicable aircraft hydraulic system specification (MIL-H-5440, AS19692, or equivalent) for proof pressure, burst pressure, and cleanliness requirements.