7050 Aluminum
Also: AA7050, UNS A97050, AlZn6CuMgZr, 7050-T7451, 7050-T7651, 7050-T74, 7050-T7452, Al 7050
7050 is the thick-plate aerospace alloy: near-7075 strength held through 150 mm (6") sections, with far better stress-corrosion resistance. Values for T7451.
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At a glance
| Density | 2.83 g/cm³ (0.102 lb/in³) |
|---|---|
| Tensile strength | 524 MPa (76 ksi) |
| Yield strength | 469 MPa (68 ksi) |
| Hardness | ~140 HB |
| Elongation | 11% |
| Modulus of elasticity | 71.7 GPa (10.4 Msi) |
| Thermal | Melts at 494-635 °C (920-1175 °F); thermal conductivity ~157 W/m·K (T7451) |
| Composition | Al, 5.7-6.7% Zn, 2.0-2.6% Cu, 1.9-2.6% Mg, 0.08-0.15% Zr, up to 0.15% Fe |
Typical values, T7451 temper (solution treated, stress-relieved by stretching, two-step overaged) for plate 25-75 mm (1-3"); minimums drop with thickness. T7651 plate is about 550 MPa (80 ksi) tensile and 490 MPa (71 ksi) yield. Confirm against the mill certificate and the purchase spec.
- MachinabilityExcellent
- Machines like 7075: clean chips, fine finish, and the stretched T7451 plate has low residual stress, so deep pockets and thin walls come out flat. The alloy of choice for large monolithic machined parts.
- WeldabilityNot recommended
- Hot-cracks under fusion welding and the temper cannot be restored; not TIG or MIG welded. Friction stir welding is used in production; job shops bolt, rivet or bond.
- FormabilityPoor
- Sold as thick plate and forgings in overaged tempers; not a forming alloy. Formed 7xxx parts are made from 7075 sheet in O or W condition.
- Corrosion resistanceFair
- General corrosion like 7075 (protect it), but far better resistance to stress-corrosion cracking and exfoliation in the T74/T76 tempers, which is the reason the alloy exists. Anodize or chem-film plus primer for service.
7050 is a zinc-magnesium-copper (7xxx series) alloy developed to fix the two weaknesses of 7075 in thick sections: quench sensitivity, which makes 7075 plate lose strength in the middle of thick sections, and stress-corrosion cracking in the peak-aged temper. Zirconium replaces chromium as the grain refiner, which lowers quench sensitivity, and the alloy is sold only in overaged T7x tempers, so it combines high strength with resistance to stress corrosion, exfoliation and fatigue crack growth through the full thickness of plate up to about 150 mm (6").
It is the standard alloy for large machined aerospace structure: bulkheads, spars, wing skins, fuselage frames and landing gear components hogged from thick plate, and for die forgings in T74 and T7452. T7451 is the balanced plate temper, with the best stress-corrosion resistance; T7651 is slightly stronger with exfoliation resistance but less SCC margin. Both are stress-relieved by stretching, which lets shops remove most of a plate without warping the part.
Machining is excellent and very similar to 7075. Everything else that limits 7075 applies here too: it is not fusion welded, it does not bend, it needs corrosion protection, and it costs more. Outside aerospace, 7050 is chosen for thick machined parts that cannot afford the through-thickness property loss or SCC risk of 7075-T651, such as large tooling plates and motorsport structural components.
Heat treatment
Precipitation hardening, done at the mill. Solution treat at about 475 °C (890 °F), quench, stretch 1.5-3% for stress relief (the 51 in T7451), then a two-step overage, roughly 120 °C (250 °F) followed by 165-175 °C (330-350 °F), to reach T74 properties. T76 is a lighter overage for higher strength with exfoliation resistance. The low quench sensitivity from zirconium is what lets thick plate reach these properties through the section. Do not re-heat-treat finished parts; buy the temper.
Tempers and conditions
- T7451 (plate, stress-corrosion resistant)
- T7651 (plate, higher strength, exfoliation resistant)
- T74 / T7452 (die and hand forgings)
- T76511 / T74511 (extrusions)
Stock forms
- Plate 12-150 mm (1/2-6"), the main form
- Die forgings and hand forgings
- Extrusions (limited, aerospace)
- Rarely sheet or bar
Relative cost
Tier 4 of 5. Roughly 2-3x the price of 7075 plate, with aerospace mill lead times and a smaller distributor network; the premium buys through-thickness properties and stress-corrosion resistance.
Typical applications
- Aircraft bulkheads, frames and wing spars machined from thick plate
- Wing skins and stringers
- Landing gear components and fittings
- Large aerospace die forgings
- Thick tooling and fixture plates that must stay stable
- Motorsport and defense structural components
Process compatibility
How 7050 takes each process, and what to specify. Each process links to its own guide and to the shops that do it.
| Process | Rating | Notes |
|---|---|---|
| CNC Machining | ExcellentExcellent | Like 7075, with lower residual stress in stretched plate; deep pockets and thin webs stay flat. The alloy for hog-outs from thick plate. |
| 5-Axis CNC Machining | ExcellentExcellent | The classic monolithic aerospace part: 90%+ of a thick plate machined away in one setup with predictable distortion. |
| Welding | Not recommendedNot recommended | Hot cracking and loss of temper under fusion welding; not TIG or MIG welded. Bolt, rivet or friction stir weld in production. |
| Waterjet Cutting | GoodGood | The usual way to rough-blank thick 7050 plate before machining; no heat-affected zone. |
| Laser Cutting | PoorPoor | Sold as thick plate, not sheet; too thick for a clean laser cut and the edge is heat-affected. Waterjet or saw the blanks. |
| Forging | GoodGood | A major aerospace die-forging alloy in T74 and T7452 (AMS 4108 family); through-thickness properties better than plate. |
| Anodizing | GoodGood | Type II works, darker and less uniform than 6061 because of the copper; the standard is anodize plus seal under aerospace finish specs. |
| Hardcoat Anodizing | FairFair | Type III builds, but thinner and softer than on 6061 and edge-sensitive; specify thickness and radius the edges. |
| Chem Film (Chromate Conversion Coating) | ExcellentExcellent | MIL-DTL-5541 chromate is the standard corrosion barrier and primer base on machined 7050 structure. |
| Shot Peening | ExcellentExcellent | Routine on fatigue-critical 7050 parts (AMS 2430); peen after final machining, before anodize or primer. |
| Heat Treating | PoorPoor | The T7451 temper is a mill process with stretching; re-solution treating a finished part warps it and loses the stress relief. Buy the temper. |
| Press Brake Forming | Not recommendedNot recommended | Thick plate in an overaged temper; it does not bend. Machine the geometry or use 7075 sheet formed in O. |
| Metal 3D Printing | PoorPoor | Not printable; high-strength printed aluminum is Scalmalloy or a vendor-modified 7xxx. Machine from plate. |
Design and sourcing tips
- Specify "7050-T7451 per AMS 4050" for machined plate parts; call out T7651 (AMS 4201) only when the extra strength is needed and the part is not loaded through the thickness.
- Use 7050 instead of 7075 when the plate is over about 50 mm (2") thick, when the part is short-transverse loaded, or when stress-corrosion cracking has bitten before.
- Design for machining: 7050 exists for parts hogged from plate, so put the geometry in one setup and let the stretched temper keep it flat.
- Do not weld it, bend it or re-heat-treat it; those operations are done in other alloys or not at all.
- Call out chem film or anodize plus primer; bare 7050 corrodes like 7075.
- Order plate with the mill cert to the AMS spec and the thickness range, because minimum properties step down as plate gets thicker.
Frequently asked questions
- What is the difference between 7050 and 7075 aluminum?
- 7050 uses zirconium instead of chromium and is sold only in overaged tempers. It keeps its strength through thick plate where 7075 loses it in the middle of the section, and it resists stress-corrosion cracking and exfoliation far better than 7075-T6. Peak strength is a little lower than 7075-T6 and the price is higher. For thin sections and bar, 7075 is fine; for thick machined structure, 7050.
- What does 7050-T7451 mean?
- T74 is a two-step overage that trades a little strength for stress-corrosion resistance; the 51 means the plate was stretched 1.5-3% after quenching to relieve residual stress. T7451 plate stays flat under heavy machining and is the standard temper for aerospace hog-outs. T7651 is the same idea with a lighter overage for higher strength and exfoliation resistance.
- Can 7050 aluminum be welded?
- Not by fusion welding. Like 7075 it hot-cracks and the heat-affected zone loses the temper permanently. Friction stir welding is used on some production aerospace structure; in a job shop the answer is bolting, riveting or bonding, or choosing 6061 or 5083 for the welded part.
- Is 7050 aluminum good for machining?
- Yes, excellent, and that is what it is bought for. It cuts like 7075 with clean chips and a fine finish, and because T7451 plate is stretched to relieve stress, large pockets and thin walls machine flat without the warping that 7075-T6 plate shows.
Processes that commonly use it
Related materials
Where to verify these values
- AMS 4050 and AMS 4201 (plate minimums by thickness)
- ASTM B209 and B247
- MMPDS (MIL-HDBK-5) design allowables
- Aluminum Association, Aluminum Standards and Data
