7175-T74
Solution heat-treated and over-aged to a level between T73 and T76 (formerly called T736). Good balance of strength, toughness and SCC resistance. Covered by AMS 4149 for die and hand forgings.
Aerospace · High-purity forgings
7175 Aerospace Aluminium Forgings
7175 is the high-purity version of 7075, made for aircraft forgings that need more strength and toughness than 7075-T73 while keeping good stress-corrosion resistance. Metline supplies 7175 die forgings, hand forgings and forged blocks in the T74 and T7452 tempers to SAE AMS 4149 and AMS 4179, with full test certification, to aerospace buyers worldwide.
- Alloy
- 7175 (high-purity 7075)
- Tempers
- T74, T7452, T66
- Thickness
- To 152 mm at heat treatment (AMS 4149)
- Specs
- AMS 4149 · AMS 4179
What 7175 forgings are and why they are used
7175 has the same zinc, magnesium, copper and chromium ranges as 7075, but iron is limited to 0.20 % and silicon to 0.15 %. With fewer coarse intermetallic particles, forgings show better fracture toughness, fatigue life and ductility in the transverse directions, which is where forgings are weakest.
7175 is also processed differently. A higher-temperature homogenising and solution treatment puts more of the alloying elements into solution, so after ageing the forging reaches higher strength for the same degree of over-ageing. That is why 7175-T74 is stronger than 7075-T73 while still offering good resistance to stress-corrosion cracking (SCC) and exfoliation.
The alloy is used for highly stressed closed-die forgings: landing-gear components, wing and fuselage fittings, engine mounts, flap tracks and helicopter rotor parts. For very thick forgings, 7050 is often preferred because its zirconium addition makes it less sensitive to quench rate; for thinner and medium sections, 7175 gives excellent strength and toughness.
7175 chemical composition (wt %)
Registered Aluminum Association limits for 7175 (UNS A97175), as used in AMS 4149 and AMS 4179. The AMS title gives the nominal chemistry 5.6 Zn - 2.5 Mg - 1.6 Cu - 0.23 Cr.
| Element | Minimum | Maximum | Comment |
|---|---|---|---|
| Silicon (Si) | — | 0.15 | Lower than 7075 (0.40) for toughness |
| Iron (Fe) | — | 0.20 | Lower than 7075 (0.50); fewer fatigue-crack origins |
| Copper (Cu) | 1.2 | 2.0 | Strength and SCC resistance |
| Manganese (Mn) | — | 0.10 | Minor |
| Magnesium (Mg) | 2.1 | 2.9 | Forms MgZn2 with zinc |
| Chromium (Cr) | 0.18 | 0.28 | Grain control |
| Zinc (Zn) | 5.1 | 6.1 | Main strengthening element |
| Titanium (Ti) | — | 0.10 | Grain refiner |
| Others, each / total | — | 0.05 / 0.15 | |
| Aluminium (Al) | Remainder |
Mechanical and physical properties
Forgings are tested in three directions: longitudinal (L, along the grain flow), long transverse (LT) and short transverse (ST). Specified minimums in AMS 4149 and AMS 4179 depend on thickness and direction. The typical values below are longitudinal values from ASM data, shown with 7075 for comparison.
| Alloy and temper (typical, L) | Tensile strength | Yield strength | Elongation | SCC resistance |
|---|---|---|---|---|
| 7175-T66 | 593 MPa / 86 ksi | 524 MPa / 76 ksi | 11 % | Low (peak aged) |
| 7175-T74 / T7452 | 525 MPa / 76 ksi | 455 MPa / 66 ksi | 11 % | Good |
| 7075-T6 forging | 572 MPa / 83 ksi | 503 MPa / 73 ksi | 11 % | Low |
| 7075-T73 forging | 505 MPa / 73 ksi | 435 MPa / 63 ksi | 13 % | Very high |
Typical values are for comparison. ST properties are lower than L; design to the specification minimums or MMPDS values.
Physical properties (T74)
- Density
- 2.80 g/cm³ (0.101 lb/in³)
- Modulus of elasticity
- About 72 GPa
- Electrical conductivity
- About 38 – 40 % IACS (used to verify the T74 condition)
- Thermal conductivity
- About 155 W/m·K
- Coefficient of thermal expansion
- About 23.4 µm/m·°C
- Melting range
- About 475 – 635 °C
7175 forging tempers explained
7175-T7452
Solution heat-treated, stress-relieved by 1 – 5 % cold compression and over-aged. The compression lowers residual quench stress so large hand forgings and blocks stay stable during machining. Covered by AMS 4179.
7175-T66
Peak-aged after the special high-temperature solution treatment. Highest strength, but SCC resistance is low, so it is limited to parts that are not loaded in the short-transverse direction.
Choosing a temper
For most loaded aircraft fittings choose T74 or T7452. T66 needs a deliberate stress-corrosion assessment, and many current programmes do not allow it for primary structure.
7175 forging types we supply
| Forging type | Typical parts | Notes |
|---|---|---|
| Closed-die (impression) forgings | Landing-gear links, fittings, brackets, engine mounts | Grain flow follows the part contour; to customer die or drawing |
| Hand (open-die) forgings | Blocks for machined fittings and frames | Usually in T7452 to keep machining distortion low |
| Forged bar and billet | Machining stock | Rectangular or round sections |
| Rolled rings | Rings, flanges, bearing housings | Circumferential grain flow |
Maximum size depends on the forging press, the heat-treatment equipment and the thickness limit of the specification (6.000 in at heat treatment for AMS 4149). Send the part envelope or drawing and we confirm what can be produced and tested.
Testing, inspection and certification
Typical requirements
- Tensile tests
- L, LT and ST directions from prolongations or a sacrificial forging, per specification
- Stress corrosion
- SCC lot acceptance per specification; conductivity and hardness on each lot
- Ultrasonic
- To AMS-STD-2154, class per drawing (often A or AA for critical parts)
- Grain flow and macro-etch
- First-article macro-etch to show grain flow follows the part contour
- Heat treatment
- To AMS 2772 or the customer process; pyrometry to AMS 2750
- Forging specification
- General requirements per AMS-QQ-A-367 where called up
- Certification
- EN 10204 3.1 certificate with chemistry, heat-treat lot and test results
Machining, finishing and SCC precautions
Machining
Machines like 7075. T7452 hand forgings have low residual stress, so heavy pocketing causes little distortion.
Shot peening
Peen fillets, bores and lugs to add compressive surface stress; this improves fatigue life and SCC resistance.
Surface protection
Anodise or conversion coat, prime and seal. Wet-install fasteners and bushings with sealant.
Design
Keep sustained tension and interference fits away from the short-transverse direction (ARP 823 practices).
Joining
Not fusion-welded; joined by bolts, rivets or interference-fit bushings.
Temperature
Avoid long exposure above about 120 °C, which over-ages the forging further.
Where 7175 forgings are used
- Landing gear: torque links, drag braces, side-stay fittings and wheels on smaller aircraft
- Wing: flap tracks, flap and slat carriages, pylon and spar fittings
- Fuselage: door frames, window frames and bulkhead fittings
- Engine and nacelle: mounts, brackets and fan-case attach fittings
- Helicopters: rotor hub components, swashplate parts and transmission fittings
- Space and defence: launcher structure fittings and missile components
7175 compared with 7075 and 7050 forgings
| Factor | 7075-T73 | 7175-T74 | 7050-T74 |
|---|---|---|---|
| Typical tensile strength | About 505 MPa | About 525 MPa | About 510 – 525 MPa |
| Toughness | Moderate | Good | Good |
| SCC resistance | Very high | Good | Good |
| Thick-section strength | Falls in heavy sections | Falls in heavy sections | Best (low quench sensitivity) |
| Main forging specification | AMS 4141 | AMS 4149 | AMS 4107 |
Use 7175-T74 when you need more strength than 7075-T73 in a medium-thickness forging. Use 7050-T74 or T7452 for thick sections. Keep 7075-T73 for parts where the highest SCC resistance outweighs strength.
How to order 7175 forgings
- SpecifyAlloy and temper, forging type, drawing or envelope dimensions, quantity and the governing specification with its revision letter (AMS 4149, AMS 4179 or AMS-QQ-A-367). 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 4149 – Die and Hand Forgings, 5.6Zn - 2.5Mg - 1.6Cu - 0.23Cr (7175-T74)
- SAE AMS 4179 – Forgings, 7175-T7452
- SAE AMS-QQ-A-367 – Aluminum Alloy Forgings
- SAE ARP 823 – Minimizing Stress-Corrosion Cracking in Wrought Heat-Treatable Aluminium Alloy Products
- AMS-STD-2154 – Inspection, Ultrasonic, Wrought Metals
- The Aluminum Association – International Alloy Designations and Chemical Composition Limits (Teal Sheets)
7175 aerospace aluminium (aluminum) forgings: FAQ
What is the difference between 7175 and 7075?
The main alloying ranges are the same, but 7175 limits iron to 0.20 % and silicon to 0.15 %, and it is solution treated at a higher temperature. The result is better toughness and fatigue life and higher strength in over-aged tempers.
What does T74 mean on a 7175 forging?
Solution heat-treated and over-aged to an intermediate level between T73 and T76. It gives a good balance of strength and stress-corrosion resistance. The temper was previously designated T736.
When should I use 7175-T7452?
For hand forgings and blocks that will be heavily machined. The cold-compression stress relief keeps residual stresses low, so the part does not distort during machining.
Which specification covers 7175-T74 forgings?
SAE AMS 4149 covers die and hand forgings in 7175-T74, 6.000 in (152 mm) and under in thickness at heat treatment.
Is 7175-T66 suitable for landing-gear parts?
Only after a careful stress-corrosion assessment. T66 is peak-aged and has low SCC resistance, so most programmes use T74 or T7452 for loaded fittings.
Do you supply 7175 forgings outside India?
Yes. Metline supplies aerospace forgings worldwide with EN 10204 3.1 certificates, full test reports and export packing.
Need 7175 forgings?
Send the drawing, temper, specification and quantity. We will confirm feasibility, testing and a delivered price.
