Aluminum 8091
AA 8091 · UNS A98091
8091 is a high-strength Al-Li-Cu-Mg alloy (A98091, AlLi2.5Cu2Mg1) developed alongside 8090 to give lower density and higher elastic modulus than conventional 2000 and 7000 series alloys.
Reference datasheet — 8091 is not in the instant-quote catalog. Upload your part and an engineer will quote it in this grade or suggest the closest stocked equivalent.
Values for the T851 condition
8091 tempers and conditions
8091 is supplied in 11 conditions, soft to hard. T851 is the default FabDigit quotes; the values on this page are for it.
Compare all 11 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Annealed | Softest condition for deep forming, straightening or intermediate machining before solution treatment. | 140 | 255 | 14 | 65 HB | 23 % IACS |
As fabricated | Mill product straight from hot working, no controlled thermal treatment — for re-heat-treatment or forging stock. | 190 | 300 | 10 | 85 HB | 25 % IACS |
Solution heat treated and naturally aged | Solution-treated and naturally aged without cold work — used where forming after heat treatment is required. | 250 | 380 | 14 | 105 HB | 17 % IACS |
Solution heat treated, cold worked and naturally aged | Sheet condition with good damage tolerance and formability, aged naturally after stretching/cold work. | 285 | 400 | 12 | 115 HB | 16 % IACS |
T3, stress relieved by stretching | Plate/bar version of T3 with stretched stress relief — low residual stress for stable machining before final ageing. | 295 | 410 | 11 | 118 HB | 16.5 % IACS |
Solution treated, stretched, overaged for toughness/SCC resistance | Overaged damage-tolerant temper for thick sections needing better short-transverse toughness and SCC resistance. | 435 | 495 | 7 | 142 HB | 21 % IACS |
Solution heat treated and artificially aged | Peak-aged condition for forgings and parts where maximum strength matters more than toughness. | 440 | 505 | 5 | 148 HB | 19 % IACS |
T6, stress relieved by stretching | Peak-aged plate with stretched stress relief — the choice for machined-from-solid, dimensionally stable structure. | 455 | 515 | 5 | 150 HB | 19 % IACS |
Solution treated, stretched, under/near-peak artificially aged | Modified ageing of stretched plate trading a little strength for better ductility and short-transverse behaviour. | 460 | 525 | 6 | 150 HB | 19 % IACS |
Solution heat treated, cold worked and artificially aged | Cold work before ageing refines the strengthening dispersion — highest strength sheet condition for Al-Li. | 465 | 525 | 5 | 152 HB | 19 % IACS |
T851Default T8, stress relieved by stretching | The standard supplied condition for 8091 plate/extrusion: near-peak strength with stretched stress relief for stable machining. | 480 | 540 | 5 | 155 HB | 19 % IACS |
What is 8091?
8091 is a high-strength Al-Li-Cu-Mg alloy (A98091, AlLi2.5Cu2Mg1) developed alongside 8090 to give lower density and higher elastic modulus than conventional 2000 and 7000 series alloys. In aged tempers such as T8 and T851 it reaches about 480 MPa yield and 540 MPa tensile at HB 155, so it is used for weight-critical aerospace sheet, plate and machined structure. The limits are low ductility (5% elongation), poor fusion weldability, moderate corrosion resistance, a 120 °C service ceiling and low commercial availability. 2024-T851 is the nearest conventional alternative when Li handling and cost cannot be justified. 8091 has a density of 2.55 g/cm³ (0.0921 lb/in³), lighter than 99% of aluminum grades. It melts at 570°C (1,058 °F). 8091 has a yield strength of 480 MPa (69.6 ksi) and a tensile strength of 540 MPa (78.3 ksi) — stronger than 95% of aluminum grades. Elongation at break is 5% and the elastic modulus is 80 GPa (11.6 Msi).
What is 8091 used for?
- aerospace fuselage skins
- structural aircraft components
- weight-critical brackets
Advantages
- High strength — 480 MPa (69.6 ksi), better than 95% of aluminum grades
- Stiff — 80 GPa (11.6 Msi), better than 95% of aluminum grades
Limitations
- Low electrical conductivity — 19 % IACS, worse than 99% of aluminum grades
- High embodied carbon — 18 kg CO₂/kg, worse than 99% of aluminum grades
- Poor heat conductor — 95 W/m·K (54.9 BTU/hr·ft·°F), worse than 98% of aluminum grades
- Limited service temperature — 120°C (248 °F), worse than 79% of aluminum grades
- Difficult to weld — 25/100, worse than 76% of aluminum grades
8091 properties
Typical room-temperature values for 8091-T851; bars are the position among aluminum grades.
Physical3
8091 has a density of 2.55 g/cm³ (0.0921 lb/in³), lighter than 99% of aluminum grades. It melts at 570°C (1,058 °F).
Mechanical13
8091 has a yield strength of 480 MPa (69.6 ksi) and a tensile strength of 540 MPa (78.3 ksi) — stronger than 95% of aluminum grades. Elongation at break is 5% and the elastic modulus is 80 GPa (11.6 Msi).
Thermal6
8091 is rated for continuous service to 120°C (248 °F). It conducts heat at 95 W/m·K (54.9 BTU/hr·ft·°F), worse than 98% of aluminum grades. Thermal expansion is 21.4 µm/m·K (11.9 µin/in·°F).
Electrical3
8091 conducts electricity at 19 % IACS, worse than 99% of aluminum grades.
Chemical & Environmental3
Corrosion resistance is fair (40/100), worse than 75% of aluminum grades.
Sustainability4
Producing a kilogram of 8091 takes about 260 MJ of energy and emits 18 kg of CO₂ — more than 99% of aluminum grades. Typical recycled content is 3%.
Manufacturability7
8091's machinability is good (65/100, better than 62% of aluminum grades); weldability poor (25/100); formability poor (30/100).
Common Calculations5
Values are nominal handbook figures for design screening. Certified mill or lot data ships with every FabDigit order on request.
Strength versus weight in the aluminum family
Yield strength against density for every aluminum grade FabDigit runs. 8091 is highlighted; hover a dot for its name, or open the interactive family chart.
Working with 8091
Is 8091 easy to machine?
Machines much like 2024-T851 with sharp carbide tools, high speed and flood coolant; the Li-oxide surface film is abrasive and fine chips/dust must be handled as reactive swarf (keep dry, no water accumulation).
Can 8091 be welded?
Poor fusion weldability — Li causes oxide entrapment, porosity and hot cracking; use friction stir welding, mechanical fastening or bonding, and pre-clean/vacuum-protect if arc welding is unavoidable.
Can 8091 be formed, bent or molded?
Form in O/T3/T4; peak-aged T6/T8 tempers have low ductility and strong anisotropy, so bend radii must be generous and orientation relative to rolling direction respected.
8091 chemical composition (wt %)
Limits by weight percent from the governing specification, written the way the spec states them — a single maximum for impurities, a range for alloying elements, and the base element as balance. Nominal is the typical mid-range value.
| Element | Spec limit (wt %) | Nominal |
|---|---|---|
| Liprimary density-reducing, modulus-raising addition | 2.4 – 2.8 | 2.6 |
| Cu | 1.6 – 2.2 | 1.9 |
| Mg | 0.5 – 1.2 | 0.9 |
| Zrgrain/subgrain control via Al3Zr | 0.04 – 0.16 | 0.12 |
| Siimpurity limit | ≤ 0.3 | |
| Feimpurity limit | ≤ 0.5 | |
| Mn | ≤ 0.1 | |
| Zn | ≤ 0.25 | |
| Ti | ≤ 0.1 | |
| Others (each) | ≤ 0.05 | |
| Others (total) | ≤ 0.15 | |
| Al | balance |
What surface finishes work on 8091?
Chromate conversion or chromic/sulfuric anodize plus primer is normal aerospace practice; control alkaline etch time to avoid Li depletion and film non-uniformity, and prime promptly to limit exfoliation risk.
Surface treatments FabDigit runs on aluminum parts — pick them in the quote configurator or call them out on the drawing. Each links to its datasheet in the surface-finish library (thickness, specs, call-out, material verdicts).
Organic Coating
Equivalent designations
Standards and trade names that resolve to Aluminum 8091 in FabDigit's catalog. Equivalence is nominal — check the exact specification when certification matters.
- UNS
- A98091
- Similar grades
- AlLi2.5Cu2Mg1
How much does 8091 cost?
8091 is a high-cost aluminum ($$$$), pricier than about 78% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
8091 — frequently asked
What is 8091 used for?
8091 is typically used for aerospace fuselage skins, structural aircraft components and weight-critical brackets. In short: low-density aerospace Al-Li; higher modulus than 2024; poor weldability, limited supply.
What is the yield strength of 8091?
8091 has a typical yield strength of 480 MPa (69.6 ksi) and a tensile strength of 540 MPa (78.3 ksi) — stronger than 95% of aluminum grades. Strength varies by condition: see the 11 listed tempers.
Is 8091 easy to machine?
Reasonably — machinability is rated good (65/100, better than 62% of aluminum grades). Machines much like 2024-T851 with sharp carbide tools, high speed and flood coolant; the Li-oxide surface film is abrasive and fine chips/dust must be handled as reactive swarf (keep dry, no water accumulation).
Can 8091 be welded?
Not readily — weldability is rated poor (25/100). Poor fusion weldability — Li causes oxide entrapment, porosity and hot cracking; use friction stir welding, mechanical fastening or bonding, and pre-clean/vacuum-protect if arc welding is unavoidable.
What surface finishes work on 8091?
Chromate conversion or chromic/sulfuric anodize plus primer is normal aerospace practice; control alkaline etch time to avoid Li depletion and film non-uniformity, and prime promptly to limit exfoliation risk.
Can 8091 be formed, bent or molded?
Form in O/T3/T4; peak-aged T6/T8 tempers have low ductility and strong anisotropy, so bend radii must be generous and orientation relative to rolling direction respected.
What is the maximum service temperature of 8091?
8091 is rated for continuous use to about 120°C (248 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between 8091-T851 and 8091-O?
T851 is the default condition — the standard supplied condition for 8091 plate/extrusion: near-peak strength with stretched stress relief for stable machining. O: softest condition for deep forming, straightening or intermediate machining before solution treatment. Yield strength is 480 MPa in T851 versus 140 MPa in O.
How much does 8091 cost?
8091 is a high-cost aluminum ($$$$), pricier than about 78% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
Sources
- International Alloy Designations and Chemical Composition Limits for Wrought Aluminum (Teal Sheets) — The Aluminum Association (2018)
- ASM Handbook Vol. 2: Properties and Selection — Nonferrous Alloys (Al-Li alloys) — ASM International (1990)
- Aluminum-Lithium Alloys: Processing, Properties and Applications — Elsevier/Butterworth-Heinemann (2014)
- Al-Li alloy 8090/8091 plate and extrusion data — British Alcan / Alcan International (1990)
Property data is compiled from published supplier and standards handbooks and normalised for comparison; hardness values on non-Brinell scales are converted approximately for charting only. Manufacturability limits are FabDigit quote-engine defaults and may be relaxed by engineering review. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.