7075 Aluminum
Also: AA7075, UNS A97075, AlZn5.5MgCu, 7075-T6, 7075-T651, 7075-T73, 7075-T7351, Al 7075, Alclad 7075
7075 is the high-strength aerospace aluminum: 572 MPa (83 ksi) tensile in T6, machines superbly, but is not weldable and stress-corrosion prone. Values for T6.
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At a glance
| Density | 2.81 g/cm³ (0.102 lb/in³) |
|---|---|
| Tensile strength | 572 MPa (83 ksi) |
| Yield strength | 503 MPa (73 ksi) |
| Hardness | 150 HB |
| Elongation | 9-11% |
| Modulus of elasticity | 71.7 GPa (10.4 Msi) |
| Thermal | Melts at 477-635 °C (890-1175 °F); thermal conductivity ~130 W/m·K; do not use above about 120 °C (250 °F) for long periods |
| Composition | Al, 5.1-6.1% Zn, 2.1-2.9% Mg, 1.2-2.0% Cu, 0.18-0.28% Cr, up to 0.5% Fe |
Typical values, T6 / T651 temper (solution treated and artificially aged). T73/T7351 (overaged for stress-corrosion resistance) is about 505 MPa (73 ksi) tensile and 435 MPa (63 ksi) yield. Confirm against the mill certificate and the purchase spec.
- MachinabilityExcellent
- One of the best-machining aluminum alloys: the hard T6 matrix breaks chips and takes a fine finish. Rated about 90-100% of the free-machining 2011 benchmark; heavy asymmetric cuts in T6 plate can release residual stress, so use T651 plate.
- WeldabilityNot recommended
- Fusion welding (TIG, MIG) hot-cracks and the heat-affected zone loses most of the T6 strength with no practical way to restore it. Friction stir welding works in production; for job-shop work, bolt, rivet, bond or switch to 6061.
- FormabilityPoor
- T6 sheet cracks on anything tighter than about 3-4x thickness inside radius. Form in the O temper or the freshly quenched W condition, then age to T6; tight bends are usually redesigned as machined or riveted joints.
- Corrosion resistanceFair
- The poorest of the common alloys bare, and T6 is susceptible to stress-corrosion cracking and exfoliation. Anodize or chem-film and prime for service; specify T73 or T7351 for parts loaded through the plate thickness.
7075 is a zinc-magnesium-copper (7xxx series) alloy that precipitation-hardens to nearly twice the strength of 6061. In T6 it matches many structural steels by number at a third of the density, which is why it is the default for highly loaded machined parts: aircraft fittings, gears in light machinery, tooling, bike and firearm components, and anything where 6061 would need to be twice as thick.
It machines beautifully. The harder matrix breaks chips cleanly and holds a fine finish, so shops often prefer it to 6061 for parts with tight tolerances. The trade is everything else: fusion welding hot-cracks and destroys the temper, the T6 temper is susceptible to stress-corrosion cracking when loaded in the short-transverse direction, bare corrosion resistance is the poorest of the common alloys, and bending T6 sheet cracks. Buy the T73 or T7351 temper when stress corrosion matters; it gives up about 10-15% strength for a large gain in SCC and exfoliation resistance.
Plate, bar and extrusions are stocked by most aluminum distributors, but not in every size 6061 comes in, and it costs roughly 1.5-2x as much per pound. For thick plate that must stay stable and crack-tolerant, 7050-T7451 is the modern aerospace successor; for welded structures, use 6061 or 5083 instead.
Heat treatment
Precipitation hardening: solution treat at about 465-480 °C (870-900 °F), water quench, then age at about 120 °C (250 °F) for 24 hours to reach T6. T73 is a two-step overage (roughly 107 °C / 225 °F then 163 °C / 325 °F) that trades strength for stress-corrosion resistance; T76 is a lighter overage for exfoliation resistance. T651/T7351 add stress relief by stretching. Annealing (O) is about 415 °C (775 °F) with a controlled slow cool. Re-heat-treating finished parts in a job shop distorts them; buy the temper you need.
Tempers and conditions
- O (annealed)
- T6
- T651 (stress-relieved plate and bar)
- T6511 (extrusions)
- T73 / T7351 (stress-corrosion resistant)
- T76 / T7651 (exfoliation resistant)
Stock forms
- Round, square, hex and flat bar
- Plate (T651, T7351)
- Sheet (bare and Alclad)
- Extruded bar, tube and profiles
- Forgings
- Seamless tube (limited sizes)
Relative cost
Tier 3 of 5. About 1.5-2x the price of 6061 per pound, and fewer stocked sizes. Machining time is similar or slightly less, so the premium is mostly material.
Typical applications
- Aircraft fittings, ribs, spars and bulkheads
- Machined gears, sprockets and shafts in light machinery
- Injection mold and blow mold tooling (in place of steel for short runs)
- Firearm receivers and frames
- Bicycle and motorsport components
- Climbing hardware, archery risers and sporting goods
- Robot arms, fixtures and any weight-critical machined structure
Process compatibility
How 7075 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 | Chips break cleanly and finishes are fine; the preferred aluminum for tight-tolerance machined parts. Use T651 plate for heavy one-sided cuts. Is 7075 aluminum easy to machine? |
| 5-Axis CNC Machining | ExcellentExcellent | The classic material for monolithic aerospace parts hogged from plate; light cutting forces suit thin walls. |
| Welding | Not recommendedNot recommended | Hot cracking and a heat-affected zone that drops to a fraction of T6 strength. Bolt, rivet or bond; design welded parts in 6061 or 5083. Can 7075 aluminum be welded? |
| Waterjet Cutting | ExcellentExcellent | Cuts plate of any stocked thickness with no heat-affected zone; the usual way to blank 7075 before machining. |
| Laser Cutting | FairFair | Sheet cuts, but the edge is heat-affected and prone to micro-cracks; waterjet or machine the profile for fatigue-critical parts. |
| Press Brake Forming | PoorPoor | T6 cracks on tight bends; form in O or W condition and age after, or make the part from 5052 or 6061 sheet. |
| Forging | GoodGood | A standard aerospace forging alloy; closed-die forgings in T6, T73 and T74 give better through-thickness properties than machined plate. |
| Aluminum Extrusion | FairFair | Extrudable, but slowly and in simpler shapes than 6063 or 6061; stock bar, tube and a few structural shapes exist, custom dies are costly. |
| Anodizing | GoodGood | Type II takes well but comes out darker and less uniform than 6061 because of the copper; dye it dark for cosmetic parts. Can 7075 aluminum be anodized? |
| Hardcoat Anodizing | GoodGood | Type III works for wear surfaces but is a little softer and more edge-sensitive than on 6061; radius the edges and specify the thickness. |
| Chem Film (Chromate Conversion Coating) | ExcellentExcellent | MIL-DTL-5541 chromate is the standard aerospace corrosion barrier and paint base on 7075; keeps conductivity. |
| Shot Peening | GoodGood | Common on fatigue-critical 7075 parts (AMS 2430); do it after machining and before anodizing. |
| Metal 3D Printing | PoorPoor | 7075 hot-cracks in laser powder bed fusion; printed high-strength aluminum is Scalmalloy or a modified 7xxx from a few vendors. Machine it instead. |
Compare 7075
Design and sourcing tips
- Call out the temper and the reason: "7075-T651" for machined plate parts, "7075-T7351" when the part is loaded through the plate thickness or sees a corrosive environment.
- Do not weld it. If an assembly must be welded, make it from 6061 and accept the lower strength, or bolt 7075 details to a welded frame.
- Specify anodize or chem film plus primer for any service outside a dry building; bare 7075 pits and exfoliates.
- Keep sustained service temperature below about 120 °C (250 °F); 7075 overages and loses strength faster than 6061 with heat.
- For thick plate parts (over 50 mm / 2"), consider 7050-T7451: it keeps its properties through the thickness where 7075 does not.
- Ask for the mill cert against AMS 4045 or ASTM B209 with the temper on the PO; "7075" without a temper can arrive as T6 when you needed T73.
Frequently asked questions
- Is 7075 aluminum stronger than steel?
- By the numbers 7075-T6 (572 MPa / 83 ksi tensile) is stronger than mild steel (about 400 MPa / 58 ksi) and close to 4140 in the annealed condition, at a third of the weight. It is not stronger than heat-treated alloy steels, and its stiffness (71.7 GPa) is a third of steel's, so a 7075 part deflects three times as much as the same steel part.
- Can 7075 aluminum be welded?
- Not by TIG or MIG in any practical sense. The alloy hot-cracks during solidification and the heat-affected zone loses most of the T6 strength, which cannot be recovered without a full re-solution treatment and quench of the whole assembly. Friction stir welding is used in production, and bolting, riveting and adhesive bonding are the job-shop answers.
- What is the difference between 7075-T6 and 7075-T73?
- T6 is peak-aged for maximum strength. T73 is overaged past the peak: it gives up about 10-15% of the tensile and yield strength but is far more resistant to stress-corrosion cracking and exfoliation. Specify T73 (T7351 for plate) for parts loaded in the short-transverse direction or used in wet or marine environments.
- Does 7075 anodize?
- Yes, Type II and Type III both work. The copper and zinc content leaves the coating darker and less uniform than on 6061, so clear cosmetic anodize on 7075 can look blotchy; dark dyes hide it. Hardcoat on 7075 is slightly softer than on 6061 and chips more easily at sharp edges.
- Is 7075 hard to machine?
- No, it is one of the easiest aluminum alloys to machine. It is harder than 6061, so chips break instead of smearing and finishes come out cleaner. The only caution is residual stress: heavy one-sided cuts in T6 plate can warp the part, so buy T651 or T7351 plate, which is stress-relieved.
Processes that commonly use it
Related materials
Where to verify these values
- ASTM B209 and B211 (mechanical property minimums by temper)
- AMS 4045 and AMS 4078
- Aluminum Association, Aluminum Standards and Data
- MMPDS (MIL-HDBK-5) design allowables
