T77
A three-step ageing treatment: a conventional low-temperature age, a short high-temperature "retrogression" step, then re-ageing. It combines near-peak strength with corrosion resistance close to overaged tempers.
Aerospace · ultra-high-strength 7xxx plate
7055-T7751 Aerospace Aluminium Plate
7055 is one of the strongest commercial aluminium plate alloys, developed for compression-dominated upper wing skins and stringers on large aircraft. In the T7751 temper it gives yield strength above 600 MPa together with useful exfoliation and stress-corrosion resistance. Metline supplies 7055-T7751 plate to AMS 4206 and matching T77511 extrusions to AMS 4337, with full certification, to aerospace buyers worldwide.
- Alloy
- 7055 (Al-8Zn-2.3Cu-2Mg-Zr)
- Temper
- T7751 plate, T77511 extrusions
- Plate thickness
- 12.7 – 38.1 mm (AMS 4206)
- Standards
- AMS 4206 · AMS 4337 · ASTM B209
What 7055 plate is designed to do
An aircraft wing bends upward in flight, so the upper skin and its stringers are loaded mainly in compression while the lower skin is in tension. Upper-wing structure is therefore sized by compressive yield strength and stability, and every gain in strength lets the designer use a thinner, lighter skin. 7055 was developed specifically for this job.
The alloy raises zinc to about 8 % with roughly 2.3 % copper and 2 % magnesium, and uses zirconium for grain control. The high solute content gives very high strength, and the T77 temper, a multi-step retrogression-and-re-ageing treatment, recovers much of the corrosion resistance that peak-aged high-zinc alloys normally lack. The result is strength above 7150-T651 with exfoliation resistance comparable to overaged tempers.
7055-T7751 plate and T77511 extrusions entered service on the Boeing 777 upper wing skins and stringers and have since been used on other large commercial aircraft. They are specialised products: buyers usually order them against a specific aircraft-manufacturer specification and part programme.
7055 chemical composition (wt %)
Registered Aluminum Association limits, used by AMS 4206 and AMS 4337. Manganese is limited to 0.05 % maximum; some published tables wrongly show 0.50 %.
| Element | Minimum | Maximum | Role in the alloy |
|---|---|---|---|
| Silicon (Si) | — | 0.10 | Held very low for toughness |
| Iron (Fe) | — | 0.15 | Held very low |
| Copper (Cu) | 2.0 | 2.6 | Strength and stress-corrosion resistance |
| Manganese (Mn) | — | 0.05 | Residual |
| Magnesium (Mg) | 1.8 | 2.3 | Forms MgZn2 with zinc |
| Chromium (Cr) | — | 0.04 | Kept low; zirconium controls grain structure |
| Zinc (Zn) | 7.6 | 8.4 | Main strengthening element; the highest of the common 7xxx plate alloys |
| Titanium (Ti) | — | 0.06 | Grain refiner |
| Zirconium (Zr) | 0.08 | 0.25 | Grain control and low quench sensitivity |
| Others, each / total | — | 0.05 / 0.15 | |
| Aluminium (Al) | Remainder | About 86.1 – 88.5 % |
Mechanical properties of 7055-T7751
Values are approximate typical figures for plate within the AMS 4206 thickness range, in the longitudinal direction. Specification minimums are lower and are set by thickness and test direction; compressive yield strength, which drives upper-wing design, is also reported in aircraft-manufacturer specifications.
| Product | Tensile strength (typical) | Yield strength (typical) | Elongation (typical) |
|---|---|---|---|
| 7055-T7751 plate (AMS 4206) | About 640 MPa / 93 ksi | About 610 MPa / 89 ksi | About 10 % |
| 7055-T77511 extrusions (AMS 4337) | About 650 MPa | About 620 MPa | About 10 % |
| For comparison: 7075-T651 plate | 570 MPa | 505 MPa | 11 % |
Some sources quote 7055 yield strength as 480 – 510 MPa. That is well below typical values for the T7751 temper and should not be used.
Physical properties
- Density
- About 2.86 g/cm³ (0.103 lb/in³)
- Modulus of elasticity
- About 71 – 72 GPa
- Electrical conductivity
- Checked as a temper-control measure; range set by the specification
- Service temperature
- Keep below about 120 °C to avoid further ageing
What T7751 means
51
The plate is stretched about 1.5 – 3 % after quenching to relieve residual stress, so it stays flat during machining of integrally stiffened panels.
Why not T6?
Peak-aged high-zinc alloys have poor exfoliation and stress-corrosion resistance. For a wing skin that sees moisture and fuel for decades, the T77 temper is essential.
7055 product forms and sizes
Supply range
- Plate (AMS 4206)
- 0.500 – 1.500 in (12.7 – 38.1 mm) thick; long lengths for wing skins by enquiry
- Extruded profiles (AMS 4337)
- 0.500 – 1.500 in thick, up to 20 in² (129 cm²) cross-section and 10 in (254 mm) circle size
- Other thicknesses
- By enquiry against the applicable customer specification
- Cut blanks
- Saw-cut pieces for development, test coupons and repair parts
- Testing
- Tensile, conductivity, exfoliation and ultrasonic inspection as specified
7055 is produced on a limited basis by specialised aerospace rolling mills, so availability and timing should be confirmed for each enquiry.
Machining, forming and protection
Machining
Machines like other high-strength 7xxx alloys: sharp carbide, high speed, flood coolant. Balance material removal between faces to control distortion on thin-skinned panels.
Forming
Wing-skin contours are produced by age forming or shot-peen forming under qualified processes; cold bending capacity is limited.
Joining
Not weldable by arc processes. Panels are fastened and sealed into the wing box.
Protection
Anodise or conversion coat and prime; fastener holes are typically sealed and many are cold expanded for fatigue life.
Where 7055 is used
- Upper wing skins: plate machined into integrally stiffened or skin-and-stringer panels
- Upper wing stringers: T77511 extrusions
- Horizontal stabiliser: compression-loaded skins and stringers
- Keel beams and floor structure: compression-critical members on large aircraft
- High-performance sports and defence: limited use where the highest aluminium strength is needed
7055 is not a general engineering alloy. It is not used for engine hot-section parts or turbine components, and claims of good weldability or "several times" the corrosion resistance of ordinary alloys are not supported.
7055 compared with 7150, 7075 and 7050
| Property | 7055-T7751 | 7150-T7751 | 7075-T651 | 7050-T7451 |
|---|---|---|---|---|
| Typical yield strength | About 610 MPa | About 570 MPa | 505 MPa | 469 MPa |
| Exfoliation resistance | Good | Good | Poor | Good |
| Fracture toughness | Moderate | Moderate–good | Moderate | Good |
| Typical role | Upper wing skin and stringers | Upper wing structure | General high-strength parts | Thick machined structure |
7055 is the right choice only where compressive strength drives the design. For thick machined parts, 7050-T7451 is tougher and more widely available; for general high-strength parts, 7075 remains cheaper.
How to order 7055 plate
- SpecifyAlloy and temper, thickness, width, length or blank sizes, quantity and the governing specification with its revision (AMS 4206 for plate, AMS 4337 for extrusions, plus any customer specification).
- ConfirmWe confirm the specification can be met, the tolerance class, any extra tests (ultrasonic class, conductivity, fracture toughness) and the delivery terms (EXW, FOB, CIF or DAP).
- InspectMaterial is checked for dimensions, straightness or flatness and surface condition; tests named on the order are carried out or arranged with an independent laboratory.
- DocumentEach lot ships with a mill test certificate to EN 10204 3.1 showing chemistry, tensile results and conductivity where specified, traceable to the cast and lot number.
- Pack and shipExport packing in sealed, moisture-protected wooden cases or on pallets, with interleaving where surfaces are critical, shipped by sea or air to your port or door.
References and standards
- SAE AMS 4206 – Aluminum Alloy Plate, 7055-T7751
- SAE AMS 4337 – Aluminum Alloy Extruded Profiles, 7055-T77511
- ASTM B209 – Standard Specification for Aluminum and Aluminum-Alloy Sheet and Plate
- The Aluminum Association – International Alloy Designations and Chemical Composition Limits (Teal Sheets)
- ASM Handbook, Vol. 2 – Properties and Selection: Nonferrous Alloys and Special-Purpose Materials
7055 aerospace aluminium (aluminum) plate: FAQ
How strong is 7055-T7751?
Typical tensile strength is about 640 MPa and yield about 610 MPa in the longitudinal direction, making it one of the strongest aluminium plate products in commercial use.
What is 7055 used for?
Mainly upper wing skins and stringers, where compressive strength sets the thickness. It also appears in horizontal stabilisers and other compression-critical structure.
Which specification covers 7055 plate?
AMS 4206 covers 7055-T7751 plate from 0.500 to 1.500 in thick. AMS 4337 covers T77511 extruded profiles.
Can 7055 be welded?
No, not by conventional arc welding. Like other high-zinc 7xxx alloys it is joined mechanically.
Is 7055 better than 7075?
It is much stronger and has better exfoliation resistance in T7751, but it is more expensive, less tough and less available. It is chosen only where its strength is needed.
Need 7055-T7751 plate?
Send thickness, size, specification and quantity. Our team will confirm availability, certification and a delivered price.
