Material Identity and Specification Family
7049 was registered with the Aluminum Association in 1968 as a high-strength Al-Zn-Mg-Cu forging alloy within the 7xxx series. Its UNS designation is A97049; the European equivalent is EN AW-7049 (EN 573-3). Unlike 7075, originally developed for rolled products and later adapted to forging, 7049 was purpose-designed for closed-die and hand forgings where the part must carry high static and fatigue loads through thick sections without the quench-sensitivity penalty that limits thicker 7075 sections.
If your part is a structural forging thicker than approximately 75 mm — a landing gear component, a bulkhead fitting, or a missile fin bracket — and 7075-T73 cannot hit the required strength in the core, 7049 in the T73 or T7352 temper is the logical next step before 7050. It delivers higher strength than 7075-T73 at comparable section thickness with acceptable stress corrosion cracking (SCC) resistance for aerospace structures per AMS 4111 and AMS 4321.
Chemical Composition per Aluminum Association
The registered limits (weight percent; single values are maxima unless a range is shown) are from Aluminum Standards and Data (Aluminum Association, 2013) and ASTM B247:
| Element | Weight % | Role |
|---|---|---|
| Zn | 7.2–8.2 | Primary strengthener through η′ (MgZn₂) precipitation |
| Mg | 2.0–2.9 | Forms MgZn₂ with Zn; drives age-hardening response |
| Cu | 1.2–1.9 | Strength & SCC resistance; higher Cu than 7075 |
| Cr | 0.10–0.22 | Grain control; suppresses recrystallization |
| Fe | 0.35 max | Impurity; excess forms Al₇Cu₂Fe that reduces toughness |
| Si | 0.25 max | Impurity; kept low to avoid Mg₂Si that consumes Mg |
| Mn | 0.20 max | Controlled low |
| Ti | 0.10 max | Grain refiner in forging stock |
| Others each | 0.05 max | — |
| Others total | 0.15 max | — |
| Al | Remainder | — |
Two features distinguish 7049 from 7075 (nominally 5.6Zn–2.5Mg–1.6Cu): the higher zinc raises the volume fraction of age-hardening precipitates, while the elevated copper shifts precipitation kinetics so overaging to T73 incurs a smaller strength penalty. The chromium addition serves the same grain-control purpose as in 7075.
Tempers and Heat Treatment
7049 is almost never machined in the as-forged (F) condition. The relevant tempers:
- T73: Solution treated and overaged for SCC resistance. Sacrifices roughly 10–15% of peak T6 strength. Default specification temper per AMS 4111.
- T7352: Solution treated, compression stress-relieved (1–3% cold work), then overaged. Essential for complex forgings where machining will release residual stresses that warp thin webs and flanges.
- T76: Intermediate overage — higher strength than T73, moderate SCC resistance. Less commonly stocked.
Solution treatment: 460–475°C, water quench. The T73 aging is two-stage: a lower-temperature nucleation stage followed by 160–175°C coarsening to the SCC-resistant condition.
Mechanical Properties
Values below are for die forgings in the longitudinal direction per ASTM E8 / ISO 6892-1, sourced from Aluminum Standards and Data (2013) and ASM Handbook Volume 2. Short-transverse properties will be lower.
| Property | 7049-T73 | 7049-T7352 | 7075-T73 (ref) |
|---|---|---|---|
| UTS (MPa) | 510–530 | ~510 | 460–505 |
| YS 0.2% (MPa) | 420–450 | ~430 | 385–435 |
| Elongation (%) | 6–7 | ~7 | 7–8 |
| Brinell Hardness | ~140 | ~140 | ~135 |
| Elastic Modulus (GPa) | 70 | 70 | 71 |
| Shear Strength (MPa) | 300–310 | ~305 | ~290 |
| Fatigue 5×10⁸, R=−1 (MPa) | 160–170 | ~165 | ~150–160 |
| Density (g/cm³) | 3.1 | 3.1 | 2.81 |
7049-T73 gains approximately 20–40 MPa yield strength over 7075-T73 at equivalent SCC resistance. Density is marginally higher (~3.1 vs. 2.81 g/cm³), yielding less than a 10% weight penalty in a typical machined component. For critical parts, the procurement specification (AMS 4111, AMS 4321) must state required properties at the test location — do not rely on handbook values alone.
Corrosion and SCC Behavior
7049’s corrosion profile reflects its position in the copper-bearing 7xxx series. The practical concerns:
- SCC: The primary reason 7049 is used in T73/T7352. Copper-bearing 7xxx alloys become SCC-susceptible in the short-transverse direction when aged to peak strength (T6). T73 overaging coarsens grain-boundary precipitates, breaking the continuous anodic path. 7049-T73 forgings tested per ASTM G47 (alternate immersion in 3.5% NaCl) typically exceed 30 days without failure at 75% of YS.
- Exfoliation: T73 temper rates EA (slight pitting) per ASTM G34 EXCO test.
- Galvanic: Contact with steel, copper alloys, or nickel alloys in wet environments drives galvanic corrosion. Use cadmium-plated or stainless fasteners with wet-install sealant.
CNC Machining: Parameters and Practical Constraints
7049 is a short-chipping alloy — it machines readily with sharp carbide tooling. The real challenge comes from the forging context: residual stresses released during material removal will distort thin-walled parts. Even in T7352, rough-machine leaving 1.5–2.0 mm stock, release from the fixture, then finish-machine.
Starting parameters below assume a rigid 40-taper CNC machining center, carbide tooling, and flood coolant. Validate with a test cut on your specific forging — these are not guaranteed production values.
| Operation | Vc (m/min) | fz (mm) | DOC (mm) | Tool |
|---|---|---|---|---|
| Rough Milling | 250–400 | 0.10–0.25 | 2–6 (ap) | 3-flute carbide, polished flute, 20–30° helix |
| Finish Milling | 350–500 | 0.05–0.12 | 0.3–0.8 (ae) | 2-flute carbide, high-helix 35–45°, uncoated polished |
| Turning | 200–350 | 0.10–0.30 | 1–4 | Carbide K10–K20, positive rake 12–18° |
| Drilling | 80–150 | 0.10–0.25 | Full D | Solid carbide, 130–140° point, peck cycle >3×D |
Coolant: Water-miscible semi-synthetic at 7–10%, high-pressure delivery (≥20 bar for pockets, ≥70 bar for deep holes). Flood cooling is the baseline — MQL is not recommended for roughing due to thermal load. Chip control: 7049 produces segmented chips that break easily, so the main hazard is recutting of trapped chips rather than birds-nesting. Good evacuation (air blast or through-coolant) is essential.
Surface Treatment
- Hard Anodizing (Type III, MIL-A-8625): Produces a dark gray coating 25–50 µm thick, 400–500 HV surface hardness. The high copper content yields a darker color than 7075 hard anodize. ~50% of coating thickness is dimensional growth — plan pre-anodize machining accordingly.
- Sulfuric Anodizing (Type II): Compatible but the copper produces a yellow-tinged coating that dyes unevenly. For appearance-critical parts, use chemical conversion coating plus paint instead.
- Conversion Coating (MIL-DTL-5541): Type I (hex-Cr) is the traditional aerospace base for paint; Type II (tri-Cr) is the RoHS alternative with slightly lower corrosion performance on copper-bearing alloys.
Applications
7049 is exclusively a forging alloy — not available as sheet, plate, tube, or bar. For parts machined from bar stock, review 7075 or 7050 instead. Typical applications:
- Aircraft forgings: Landing gear components, wing attachment fittings, bulkhead chords — where 7075-T73 cannot meet strength at minimum section.
- Missile/ordnance: Fin brackets, actuator housings, structural frames requiring the strength–SCC balance at moderate section thickness.
- Motorsport: Suspension uprights, control arms, brake caliper bodies where forged 7075 is borderline and 7050 is cost-prohibitive.
7049 vs. 7050: When the Upgrade Is Justified
| Criterion | 7049-T73 | 7050-T74 |
|---|---|---|
| Longitudinal YS | 420–450 MPa | 440–470 MPa |
| SCC resistance (ST) | Good (T73) | Very good (T74) |
| Fracture toughness | Moderate — adequate for non-DT parts | Higher — preferred for damage-tolerant design |
| Quench sensitivity | Moderate (~125 mm max) | Low (~150 mm max) |
| Relative cost | Closer to 7075 | 15–25% premium |
Choose 7049 when the section is under ~125 mm, the part is not fracture-critical, and moderate SCC resistance is acceptable. Choose 7050 for damage-tolerant designs or thicker sections. A related alloy, 7149, was developed as a toughness-optimized variant of 7049 with tighter Fe and Si limits — it is not a direct substitute; check the procurement specification.
RFQ Checklist for 7049 CNC Machined Forgings
Provide the following at a minimum. Missing items add lead time and increase first-article risk:
- Forging drawing/CAD model including envelope, parting line, draft angles, fillet radii, and test coupon location. Do not send a finished-part model and assume the forging house will derive the forging geometry.
- Material specification: AMS 4111 (die forgings) or AMS 4321 (hand forgings). State temper unambiguously — T73 or T7352, not “overaged.”
- Grain flow diagram: Show required grain flow relative to the principal load axis. Wrong grain orientation can halve effective fatigue strength.
- Test specimen location and required properties: State which location, which direction (L, LT, ST), and which values. A handbook table is not a procurement requirement.
- SCC testing (if required): ASTM G47 acceptance criteria, test direction, and threshold stress as % of YS.
- Surface protection: Anodize type/thickness, conversion coating class, primer spec, and masking requirements.
- Inspection and documentation: Dimensional report, material cert (EN 10204 3.1), NDT — penetrant per ASTM E1417, ultrasonic per AMS-STD-2154 for forging quality.
- Quantity, delivery schedule, packaging: With or without temporary corrosion protection, with or without final surface treatment.
Technical references: Aluminum Association, Aluminum Standards and Data (2013); ASTM B247, Standard Specification for Aluminum and Aluminum-Alloy Die Forgings, Hand Forgings, and Rolled Ring Forgings; AMS 4111, Aluminum Alloy Forgings 7.2Zn–2.2Mg–1.6Cu–0.10Cr (7049-T73) Solution and Precipitation Heat Treated; ASM Handbook Vol. 2, Properties and Selection: Nonferrous Alloys and Special-Purpose Materials (1993).
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