6061 Aluminum
Also: AA6061, UNS A96061, AlMg1SiCu, 6061-T6, 6061-T651, Al 6061
6061 is the general-purpose aluminum alloy: strong enough for structure, easy to machine, weldable, corrosion-resistant and stocked in every form. Values for T6.
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At a glance
| Density | 2.7 g/cm³ (0.0975 lb/in³) |
|---|---|
| Tensile strength | 310 MPa (45 ksi) |
| Yield strength | 276 MPa (40 ksi) |
| Hardness | 95 HB |
| Elongation | 12-17% |
| Modulus of elasticity | 69 GPa (10.0 Msi) |
| Thermal | Melts at 582-652 °C (1080-1205 °F); thermal conductivity ~167 W/m·K |
| Composition | Al, 0.8-1.2% Mg, 0.4-0.8% Si, 0.15-0.4% Cu, 0.04-0.35% Cr, up to 0.7% Fe |
Typical values, T6 / T651 temper (solution treated and artificially aged). Confirm against the mill certificate and the purchase spec.
- MachinabilityGood
- Machines fast and cleanly in T6 with sharp, polished tooling; the O and T4 tempers are gummy and smear. Rated around 90% of the free-machining 2011 benchmark.
- WeldabilityExcellent
- Welds readily by TIG and MIG with 4043 or 5356 filler. Expect the heat-affected zone of a T6 part to lose 30-40% of its strength unless it is re-heat-treated after welding.
- FormabilityGood
- Form in O or T4 and age afterwards for tight bends; T6 sheet needs an inside radius of about 1.5-2.5x thickness and cracks on tight bends.
- Corrosion resistanceGood
- Good in atmosphere and fresh water; anodize or chem-film for marine and coastal service, and isolate it from steel and carbon fiber to avoid galvanic attack.
6061 is a magnesium-silicon (6xxx series) aluminum alloy that precipitation-hardens to a useful strength while staying easy to machine, weld and anodize. It is the alloy most U.S. machine shops reach for by default, and the one most often stocked in bar, plate, sheet, tube and extruded shapes, so it is usually the cheapest aluminum to buy in small quantities and the fastest to get.
In the T6 temper it offers about 310 MPa (45 ksi) tensile strength at 2.70 g/cm³, a third the density of steel. That is enough for brackets, frames, fixtures, enclosures, manifolds and most machined prototypes. It is not the strongest aluminum: 7075 is nearly twice as strong, and 2024 has better fatigue performance, but both weld poorly and cost more.
Its main limitations are the loss of strength in the heat-affected zone when it is welded (a T6 weld zone drops to roughly the O-temper strength unless the part is re-solution-treated and aged), a fatigue endurance limit that is low relative to steel, and softness under wear. For sliding contact, hardcoat anodize it or use a bushing.
Heat treatment
Precipitation hardening: solution treat at about 530 °C (985 °F), water quench, then age at about 175 °C (350 °F) for 8 hours to reach T6. T651 is T6 with stress relief by stretching, which matters for plate that must stay flat after machining. Annealing (O) is about 415 °C (775 °F) with a slow cool.
Tempers and conditions
- O (annealed)
- T4
- T6
- T651 (stress-relieved plate and bar)
- T6511 (extrusions)
Stock forms
- Round, square, hex and flat bar
- Plate (T651)
- Sheet
- Tube and pipe
- Extruded angle, channel and custom profiles
Relative cost
Tier 2 of 5. The baseline aluminum. Per pound it costs several times mild steel, but at a third of the density a part often costs about the same in material. Cheapest in extruded shapes.
Typical applications
- Machined brackets, fixtures and housings
- Structural frames, truck bodies and trailers
- Enclosures and chassis
- Bicycle frames and sporting goods
- Marine and RV fittings
- Hydraulic and pneumatic manifolds
- Aircraft and automotive fittings where 2024 or 7075 strength is not needed
Process compatibility
How 6061 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 | GoodGood | Fast and clean in T6 with sharp tooling; the default prototype material. |
| Welding | ExcellentExcellent | TIG or MIG with 4043/5356 filler; the T6 weld zone drops to about annealed strength. Can 6061 aluminum be welded? |
| Laser Cutting | GoodGood | Fiber lasers cut sheet and plate to about 12 mm (1/2") cleanly; nitrogen assist for a dross-free edge. |
| Press Brake Forming | GoodGood | Bend T6 sheet at 1.5-2.5x thickness inside radius, or form in O/T4 and age after. Can 6061-T6 aluminum be bent? |
| Aluminum Extrusion | ExcellentExcellent | The most common extrusion alloy after 6063; T6 or T6511 profiles from stock dies. |
| Anodizing | ExcellentExcellent | Clear or dyed Type II, uniform colour; the standard finish for 6061 (MIL-A-8625 Type II). Can 6061 aluminum be anodized? |
| Hardcoat Anodizing | GoodGood | 25-75 um (0.001-0.003") of hard oxide for wear surfaces; specify Class 1 and radius the edges. |
| Chem Film (Chromate Conversion Coating) | ExcellentExcellent | Chromate conversion keeps conductivity and is the usual paint base (MIL-DTL-5541). |
| Powder Coating | GoodGood | Needs a chromate or chrome-free pretreatment for adhesion; masks fine features. Can 6061 aluminum be powder coated? |
| Electroless Nickel Plating | GoodGood | After a zincate pretreatment; for wear, solderability and a bright finish. Can aluminum be nickel plated? |
| Bead Blasting | GoodGood | A matte, uniform surface that hides machining marks before anodizing. |
| Metal 3D Printing | FairFair | Not printable as 6061; printed aluminum is AlSi10Mg, then finish-machined. Machine 6061 instead below a few hundred pieces. |
Compare 6061
Design and sourcing tips
- Call out the temper: "6061-T6" for bar, sheet and extrusions, "6061-T651" for plate that must stay flat after heavy machining.
- Do not count on T6 strength across a weld; design welded joints to the O-temper numbers or specify post-weld heat treatment.
- Use 2024 or 7075 when the part is strength-limited and will not be welded; use 5052 for sheet metal that is formed and welded.
- Specify MIL-A-8625 Type II Class 2 with the dye colour for cosmetic parts; add "mask threads and press fits" so plating growth does not close them.
- For wear surfaces, specify Type III hardcoat with a thickness and note that half of it grows outward from the machined surface.
- Ask for a mill certificate when the drawing calls a spec (AMS 4027, ASTM B209): 6061 is often substituted by 6082 or 6063 extrusions unless the spec is on the PO.
Frequently asked questions
- What is the difference between 6061-T6 and 6061-T651?
- Both are solution treated and artificially aged to the same strength. T651 is additionally stress-relieved by stretching 1-3% after quenching, which removes most of the residual stress from the quench. Specify T651 for plate and bar that will be machined heavily on one side, because it stays flat; T6 is fine for extrusions, sheet and light machining.
- Is 6061 aluminum strong?
- For an aluminum alloy it is moderately strong: about 310 MPa (45 ksi) tensile and 276 MPa (40 ksi) yield in T6, similar to mild steel by number but at a third of the weight. 7075-T6 reaches 572 MPa (83 ksi). Most brackets, frames and fixtures are stiffness-limited, not strength-limited, so 6061 is usually enough.
- Can 6061 be welded?
- Yes, easily, with 4043 or 5356 filler by TIG or MIG. The catch is strength: the heat-affected zone of a T6 part falls to roughly annealed strength, so a welded 6061 structure is designed to about 165 MPa (24 ksi) tensile in the weld zone unless the assembly is re-solution-treated and aged after welding.
- Does 6061 anodize well?
- Very well. 6061 takes a clear or dyed Type II anodize with uniform colour, and a Type III hardcoat for wear. Colour match between lots depends on the anodizer keeping the same alloy and temper across the batch, so keep one alloy per assembly if the parts must match.
Processes that commonly use it
Related materials
Where to verify these values
- ASTM B209 and B221 (mechanical property minimums by temper)
- AMS 4027 and AMS 4117
- Aluminum Association, Aluminum Standards and Data
- MMPDS (MIL-HDBK-5) design allowables
