6061 Aluminium
6061 is a heat-treatable aluminium alloy strengthened with magnesium and silicon, and one of the most common aluminium alloys for general-purpose use (in the US it is called 6061 aluminum). In the T6 temper it reaches a tensile strength of about 310 MPa (45 ksi) at roughly a third of the density of steel.
Updated 28 Sep 2026 · 5 min read · By Wyntek
What 6061 aluminium is
6061 belongs to the 6xxx family of wrought aluminium alloys, which get their strength from magnesium and silicon. It contains 0.8 to 1.2% magnesium and 0.4 to 0.8% silicon, with small amounts of copper and chromium. It is precipitation hardened: heat treatment dissolves the alloying elements, and controlled ageing then forms fine particles that strengthen the metal.
The alloy is sold as EN AW-6061 in Europe and carries the number A96061 in the Unified Numbering System. US aluminium producer Kaiser describes it as a good all-purpose alloy with good corrosion resistance, medium strength, and good machining characteristics, which is why it is a common starting point for brackets, plates, housings, and fixtures.
Tempers: what T6 and T651 mean
The letters after 6061 give the temper, the heat treatment the metal has received. The same alloy is two and a half times stronger in T6 than when annealed.
| Temper | Condition | Tensile strength | Yield strength | Elongation | Hardness |
|---|---|---|---|---|---|
| O | Annealed, fully soft | 124 MPa (18 ksi) | 55 MPa (8 ksi) | 25% | 30 HB |
| T4 | Solution heat treated, naturally aged | 241 MPa (35 ksi) | 145 MPa (21 ksi) | 22% | 65 HB |
| T6 | Solution heat treated, artificially aged | 310 MPa (45 ksi) | 276 MPa (40 ksi) | 12% | 95 HB |
T651 material is T6 that was also stretched after quenching to relieve internal stress, so it moves less as material is machined away.
Typical properties of 6061-T6
| Property | Typical value | What it means for a part |
|---|---|---|
| Tensile strength | 310 MPa (45 ksi) | About five times the in-plane strength of printed nylon |
| Yield strength | 276 MPa (40 ksi) | Stays elastic under loads that would bend a plastic part |
| Stiffness (elastic modulus) | 68 to 70 GPa | About a third as stiff as steel, and over 20 times stiffer than printed PLA |
| Hardness | 95 HB | Resists dents, but softer than steel |
| Fatigue strength | 97 MPa (14 ksi) at 500 million cycles | Keep repeated loads well below the yield strength |
| Thermal conductivity | 167 W/m·K | Spreads heat well, useful for mounts around electronics |
| Thermal expansion | 23.6 µm/m·K | Grows about twice as much as carbon steel when heated |
| Density | 2.70 g/cm³ (0.098 lb/in³) | About a third of the weight of the same part in steel |
Values are typical figures from Kaiser and Aalco. Guaranteed minimums sit lower and depend on the product form, size, and standard. A commonly quoted T6 minimum is 290 MPa (42 ksi) tensile and 240 MPa (35 ksi) yield, while Aalco quotes 260 MPa tensile and 240 MPa proof stress for T6 extrusions. Check the specification if a design depends on them.
Where 6061 works well
- Brackets, plates, mounts, and fixtures that need to be stiff, light, and dimensionally stable.
- Housings and enclosures, including ones that carry heat away from electronics.
- Prototypes of parts that will be made in aluminium later, so tests use the real material.
- Parts used outdoors or in damp air. Kaiser rates 6061 suitable for industrial and seacoast atmospheres without protection.
Limits to design around
- Welding weakens it. Near a weld, 6061-T6 falls back to roughly T4 properties, a loss of about 40% in strength.
- It is about a third as stiff as steel. The same shape under the same load deflects about three times as much.
- It is softer than steel. Sliding surfaces, wear points, and threads that are used over and over last longer in steel.
- It expands about twice as much as carbon steel with temperature, which matters where aluminium and steel parts fit together.
6061-T6 compared with steel and printed plastic
| Material | Density | Stiffness | Tensile strength | Same part weighs |
|---|---|---|---|---|
| 6061-T6 aluminium | 2.70 g/cm³ | 68 GPa | 310 MPa | Baseline |
| 1018 carbon steel | 7.87 g/cm³ | 205 GPa | 440 MPa | About 2.9 times as much |
| 304 stainless steel | 7.9 g/cm³ | 200 GPa | About 600 MPa | About 2.9 times as much |
| Printed PETG | 1.27 g/cm³ | 1.7 to 1.9 GPa | 46 to 50 MPa | About half as much |
For its weight, 6061-T6 is about as stiff as steel and stronger than common machining steels such as 1018 and 304. Steel still wins where absolute strength, hardness, or wear resistance matters, and printed plastics are the lower-cost choice for parts that do not need metal.
Designing parts to machine in 6061
- Give internal corners a radius. Milling cutters are round, so an inside vertical corner can never be perfectly sharp.
- Keep pockets shallow relative to their width. Deep, narrow pockets need long, thin cutters that deflect and vibrate.
- Avoid very thin walls and tall, unsupported ribs, which flex under the cutter.
- Apply tight tolerances only where parts mate. Looser tolerances machine faster.
- Upload a STEP file. It keeps exact curves and faces, where a mesh file approximates them with triangles.
At Wyntek
Wyntek machines aluminium on Pro plans and up. Upload your file, choose CNC machining and aluminium, and pick a tolerance class: ±0.2 mm (±0.008 in) standard, ±0.1 mm (±0.004 in) tight, or ±0.05 mm (±0.002 in) precision for suitable features. You see the price in US dollars before you submit, and every part is scanned and inspected before it ships.
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