T7
Solution heat-treated and over-aged beyond peak strength, in two ageing steps, to raise resistance to stress corrosion and exfoliation.
Aerospace · High-zinc extrusions
7149-T73511 Aerospace Aluminium Extrusions
7149 is a high-purity, high-zinc version of 7049, extruded and over-aged to the T73511 temper for aircraft parts that need high strength together with strong resistance to stress-corrosion cracking. Metline supplies 7149-T73511 bars, rods and profiles to SAE AMS 4343, and the related 7049 grade, to aerospace manufacturers worldwide.
- Alloy
- 7149 (Al-Zn-Mg-Cu)
- Temper
- T73511
- Spec
- AMS 4343
- Size
- Up to 127 mm least thickness
What 7149 is and where it fits
7149 shares the zinc-rich chemistry of 7049 (about 7.7 % zinc), but with tighter limits on iron and silicon. Fewer iron- and silicon-rich particles mean better fracture toughness and fatigue behaviour, which is why aerospace extrusions moved from 7049 to 7149.
The alloy is used almost entirely in the over-aged T73 family. In extrusions this is T73511: solution heat-treated, stress-relieved by stretching, straightened and over-aged. SAE AMS 4343 describes the product as suited to structural parts that need high strength, moderate fatigue strength, good stress-corrosion resistance and good fracture toughness. That combination suits thick-walled sections in landing-gear structures, wing and fuselage fittings machined from extruded bar, and heavy stringers or beams.
Compared with 7075-T73511, 7149-T73511 gives higher strength at the same stress-corrosion rating, because the extra zinc allows more strengthening precipitate even after over-ageing. Compared with 7050, it is less common and is usually chosen because an existing drawing or programme already names it.
7149 chemical composition compared with 7049 (wt %)
| Element | 7149 | 7049 | Effect |
|---|---|---|---|
| Silicon (Si) | ≤ 0.15 | ≤ 0.25 | Lower Si and Fe in 7149 improve toughness |
| Iron (Fe) | ≤ 0.20 | ≤ 0.35 | Coarse Fe-rich particles start fatigue cracks |
| Copper (Cu) | 1.2 – 1.9 | 1.2 – 1.9 | Strength and SCC resistance |
| Manganese (Mn) | ≤ 0.20 | ≤ 0.20 | Minor |
| Magnesium (Mg) | 2.0 – 2.9 | 2.0 – 2.9 | Forms MgZn2 with zinc |
| Chromium (Cr) | 0.10 – 0.22 | 0.10 – 0.22 | Grain control |
| Zinc (Zn) | 7.2 – 8.2 | 7.2 – 8.2 | Main strengthening element |
| Titanium (Ti) | ≤ 0.10 | ≤ 0.10 | Grain refiner |
| Others, each / total | 0.05 / 0.15 | 0.05 / 0.15 | |
| Aluminium (Al) | Remainder | Remainder |
Registered Aluminum Association limits. The UNS number for 7149 is A97149; some old data sheets list an incorrect number, so check it on certificates.
Mechanical and physical properties of 7149-T73511
Specified minimum properties in AMS 4343 depend on the thickness of the section and the test direction. The values below are typical for the 7049/7149-T73 class and are given for comparison only; use the AMS minimums or MMPDS design values for structural calculations.
| Property | 7149-T73511 (typical) | 7075-T73511 (typical) | 7050-T76511 (typical) |
|---|---|---|---|
| Tensile strength | About 515 – 540 MPa | About 505 MPa | About 550 MPa |
| Yield strength (0.2 %) | About 450 – 470 MPa | About 435 MPa | About 490 MPa |
| Elongation | About 10 – 12 % | About 12 % | About 10 % |
| Stress-corrosion rating | Very good (T73) | Very good (T73) | Moderate (T76) |
Physical properties
- Density
- About 2.84 g/cm³ (0.103 lb/in³)
- Modulus of elasticity
- About 72 GPa
- Electrical conductivity
- About 38 – 41 % IACS in T73 (used to verify over-ageing)
- Coefficient of thermal expansion
- About 23.4 µm/m·°C
- Melting range
- About 465 – 625 °C
Data sheets claiming that 7149 is "weldable by conventional methods" or suitable for marine immersion are wrong. Like all high-strength 7xxx alloys, it is not fusion-welded and needs corrosion protection in service.
What T73511 means
3
The degree of over-ageing that gives the highest SCC resistance (T73), compared with T74 and T76 which keep more strength.
51
Stress-relieved by controlled stretching after quenching, typically 1 – 3 % permanent set, so the section stays straight when machined.
1
Minor straightening allowed after stretching to meet straightness tolerances.
Other 7149 tempers that appear on old data sheets (T6, T651, T7351, T7451) are mostly plate or forging designations or are not covered by a current aerospace specification. For extrusions, order T73511 to AMS 4343 unless the drawing states otherwise.
7149 extrusion shapes and size range
| Product | Typical range | Notes |
|---|---|---|
| Round bar and rod | About 10 – 127 mm diameter | Machining stock for fittings and lugs |
| Rectangular and square bar | Up to 127 mm least thickness | Width depends on the extrusion press and die |
| Open profiles (angle, T, Z, J, channel) | Per customer drawing | Stringers, chords and frame sections |
| Tube | Per drawing | Only where the section is extrudable in 7149 |
| Lengths | Mill lengths or cut to size | Long lengths are limited by stretching equipment |
Weight of 7149 round bar per metre (density 2.84 g/cm³):
| Diameter (mm) | kg per metre | kg per 3 m bar |
|---|---|---|
| 12 | 0.32 | 1.0 |
| 16 | 0.57 | 1.7 |
| 20 | 0.89 | 2.7 |
| 25 | 1.39 | 4.2 |
| 30 | 2.01 | 6.0 |
| 40 | 3.57 | 10.7 |
| 50 | 5.58 | 16.7 |
| 60 | 8.03 | 24.1 |
| 75 | 12.55 | 37.6 |
| 90 | 18.07 | 54.2 |
| 100 | 22.31 | 66.9 |
| 127 | 35.98 | 107.9 |
Tolerances, testing and certification
Typical AMS 4343 order
- Dimensional tolerances
- To ANSI H35.2 extrusion tolerances, or tighter per drawing
- Tensile testing
- Longitudinal tests per lot; transverse tests on thicker sections as required
- Stress-corrosion
- Alternate-immersion SCC test lots as required by the specification
- Conductivity
- Eddy-current conductivity on each lot to confirm the T73 condition
- Ultrasonic inspection
- To AMS-STD-2154 on thicker bars when specified
- Certification
- EN 10204 3.1 certificate with chemistry, properties and lot traceability
Machining, joining and finishing
Machining
Machines like 7075-T73: good chip control and surface finish. Because T73511 is stress-relieved, distortion is low even when most of the section is machined away.
Joining
Not fusion-welded. Parts are bolted or riveted; interference-fit fasteners are acceptable in T73 tempers that have good SCC resistance.
Surface protection
Sulphuric or chromic acid anodise, or conversion coating plus primer. Wet-install fasteners with sealant to prevent galvanic corrosion.
Heat exposure
Avoid temperatures above about 120 °C for long periods; further ageing reduces strength.
Where 7149 extrusions are used
- Landing-gear structure: machined fittings and links from heavy extruded bar
- Wing and fuselage: spar caps, chords, stringers and heavy attach fittings
- Helicopters: transmission-support fittings and frame members
- Defence: high-strength extruded sections in vehicles and munitions where SCC resistance is required
How to order 7149 extrusions
- SpecifyAlloy and temper, section drawing or bar size, length, quantity and the governing specification with its revision letter (AMS 4343). Add any customer or prime-contractor material specification that sits on top of the AMS.
- ConfirmWe confirm the specification can be met, the tolerance class, any extra tests (ultrasonic class, conductivity, fracture toughness, grain flow) and the delivery terms (EXW, FOB, CIF or DAP).
- InspectMaterial is checked for dimensions, surface condition and marking; 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 giving chemistry, mechanical results and heat-treatment lot, traceable to the cast number.
- Pack and shipExport packing in sealed, moisture-protected wooden cases or on pallets, shipped by sea or air to your port or door.
References and standards
- SAE AMS 4343 – Extrusions, 7.7Zn - 2.4Mg - 1.6Cu - 0.16Cr (7149-T73511)
- SAE AMS 4320 – Forgings, 7149-T73 (stabilised)
- ANSI H35.2 – Dimensional Tolerances for Aluminum Mill Products
- The Aluminum Association – International Alloy Designations and Chemical Composition Limits (Teal Sheets)
- MMPDS – Metallic Materials Properties Development and Standardization (successor to MIL-HDBK-5)
7149 aerospace aluminium (aluminum) extrusions: FAQ
What is the difference between 7149 and 7049?
They have the same main alloying ranges (about 7.7 % Zn, 2.4 % Mg, 1.6 % Cu). 7149 limits iron to 0.20 % and silicon to 0.15 %, against 0.35 % and 0.25 % for 7049, which improves fracture toughness and fatigue behaviour.
Which specification covers 7149 extrusions?
SAE AMS 4343 covers 7149-T73511 extruded bars, rods, wire, shapes and tubing up to 5.000 in (127 mm) nominal diameter or least thickness.
Is 7149 available as forgings?
Its forging specification, AMS 4320 (7149-T73), has been stabilised because no producers could be found. For forgings, 7050-T74 or 7175-T74 is the usual alternative.
Can 7149-T73511 be welded?
No. It is joined mechanically. Fusion welding causes cracking and a large loss of strength.
Why is T73511 used instead of T6511?
The over-aged T73 condition gives very high resistance to stress-corrosion cracking. The peak-aged T6 condition is stronger but too susceptible to SCC for most loaded aircraft parts made from high-zinc alloys.
Do you supply 7149 extrusions worldwide?
Yes. Metline ships to aerospace customers worldwide with EN 10204 3.1 certificates and export packing.
Need 7149-T73511 extrusions?
Send the section, length, quantity and specification. We will confirm availability, testing and a delivered price.
