Cutting and drilling
Saw with a fine-pitch carbide blade and lubricant. T6 drills and taps cleanly; for thin walls use rivet nuts or threaded inserts instead of tapping directly into the wall.
Structural square hollow section
6061 Aluminium Square Tube (T6)
6061-T6 square tube is the standard choice when a frame, chassis or support needs real structural strength from a light, weldable and corrosion-resistant hollow section. Metline supplies 6061 square tubing (6061 aluminum square tubing in the US) from 10 mm to over 200 mm across, in sharp or radiused corners, cut to length and certified to ASTM or EN standards, to buyers worldwide.
- Alloy
- 6061 (Al-Mg-Si-Cu)
- Tempers
- T6, T6511, T4, O
- Sizes
- 10 × 10 to 250 × 250 mm
- Standards
- ASTM B221 · B429 · EN 755
What is 6061 square tube?
6061 square tube is an extruded hollow section with four equal sides, made from the heat-treatable 6061 alloy and normally supplied in the T6 temper. It carries roughly 50 % more load than the same section in 6063-T6, which is why it is used for structures rather than trim.
Square tube is extruded either over a mandrel (seamless) or through a porthole die, where the metal splits around a bridge and re-joins under pressure inside the die. Porthole tube has longitudinal seam welds that are metallurgically sound for structural work and is how most square sections are made. Seamless square tube is specified when the part must hold internal pressure or pass a flattening or expansion test.
After extrusion the tube is solution heat-treated (usually on the press with a water or air quench), stretched to straighten it and relieve stresses, and artificially aged to T6. The result is a section with a flat-to-flat torsional stiffness close to a round tube of the same weight, but with flat faces that make bolting, welding gussets, mounting panels and clamping in a vice simple.
6061 chemical composition (wt %)
Composition limits are the registered Aluminum Association values, followed by ASTM B221 and EN 573-3 for EN AW-6061. The mill certificate with each lot shows the measured analysis.
| Element | Min | Max | Why it matters |
|---|---|---|---|
| Silicon (Si) | 0.40 | 0.80 | Forms Mg2Si with magnesium, the strengthening phase |
| Iron (Fe) | — | 0.70 | Impurity; kept low for toughness |
| Copper (Cu) | 0.15 | 0.40 | Raises strength above 6063 |
| Manganese (Mn) | — | 0.15 | Grain control |
| Magnesium (Mg) | 0.80 | 1.20 | Main strengthening element |
| Chromium (Cr) | 0.04 | 0.35 | Controls grain growth; aids stress-corrosion resistance |
| Zinc (Zn) | — | 0.25 | Impurity |
| Titanium (Ti) | — | 0.15 | Grain refiner |
| Others each / total | — | 0.05 / 0.15 | |
| Aluminium | Remainder |
Mechanical properties of 6061 square tube
Design to the specified minimums of the standard on your order; the typical figures show what extruded T6 tube usually achieves in testing. Wall thickness matters: minimums in ASTM B221 and EN 755-2 apply to defined wall ranges.
| Temper / basis | Tensile strength | Yield strength (0.2 %) | Elongation | Hardness |
|---|---|---|---|---|
| O, typical | 125 MPa / 18 ksi | 55 MPa / 8 ksi | 25 % | 30 HB |
| T4, typical | 240 MPa / 35 ksi | 145 MPa / 21 ksi | 22 % | 65 HB |
| T6 / T6511, typical | 310 MPa / 45 ksi | 276 MPa / 40 ksi | 12 % | 95 HB |
| T6 extruded, ASTM B221 minimum | 260 MPa / 38 ksi | 240 MPa / 35 ksi | 8 – 10 % | — |
| T6 extruded, EN 755-2 minimum (thin walls) | 260 MPa | 240 MPa | 8 – 10 % | — |
| T6 after welding (ADM design value) | 165 MPa / 24 ksi | — | — | — |
Physical properties
- Density
- 2.70 g/cm³
- Modulus of elasticity
- 68.9 GPa
- Thermal conductivity (T6)
- 167 W/m·K
- Electrical conductivity (T6)
- 43 % IACS
- Thermal expansion
- 23.6 µm/m·°C (20 – 100 °C)
- Melting range
- 582 – 652 °C
Standards and international equivalents
| System | Designation | Typical tube standard |
|---|---|---|
| ASTM / Aluminum Association | 6061-T6 | ASTM B221 (extruded), B429 (structural pipe and tube), B241 (seamless) |
| Aerospace | 6061-T6 / T6511 | AMS 4150, AMS-QQ-A-200/8 (extrusions) |
| UNS | A96061 | — |
| Europe | EN AW-6061 (AlMg1SiCu) | EN 755-2 properties; EN 755-8 porthole and EN 755-7 seamless tolerances |
| Germany | 3.3211 | DIN EN 755 |
| Japan | A6061S / A6061TE | JIS H4100, JIS H4080 |
| India | 65032 | IS 733 |
Seamless and porthole tube are both accepted under ASTM B221; specify "seamless" on the order if your application requires it.
6061 square tube sizes, weights and section properties
Supply range
- Outside size
- 10 × 10 mm to about 250 × 250 mm; imperial 1/2 in to 8 in
- Wall thickness
- 1.0 – 12 mm (0.035 – 0.500 in)
- Corners
- Sharp outside corners or radiused corners, as specified
- Length
- 3 m, 5.8 m and 6 m mill lengths; cut-to-length pieces on request
- Finish
- Mill finish, anodised, brushed or powder coated
Weights below assume sharp corners and a density of 2.70 g/cm³; radiused corners reduce the weight slightly. Section modulus (Z) is about either principal axis and is what you use for bending stress (σ = M / Z).
| Size (mm) | Wall (mm) | kg/m | I (cm⁴) | Z (cm³) |
|---|---|---|---|---|
| 20 × 20 | 2 | 0.39 | 0.8 | 0.79 |
| 25 × 25 | 2 | 0.50 | 1.6 | 1.31 |
| 25 × 25 | 3 | 0.71 | 2.2 | 1.74 |
| 30 × 30 | 3 | 0.87 | 4.0 | 2.66 |
| 40 × 40 | 3 | 1.20 | 10.2 | 5.10 |
| 40 × 40 | 4 | 1.56 | 12.6 | 6.30 |
| 50 × 50 | 3 | 1.52 | 20.8 | 8.34 |
| 50 × 50 | 5 | 2.43 | 30.8 | 12.30 |
| 60 × 60 | 4 | 2.42 | 47.1 | 15.69 |
| 75 × 75 | 5 | 3.78 | 114.9 | 30.64 |
| 80 × 80 | 5 | 4.05 | 141.2 | 35.31 |
| 100 × 100 | 6 | 6.09 | 333.6 | 66.72 |
| 120 × 120 | 6 | 7.39 | 594.3 | 99.04 |
| 150 × 150 | 8 | 12.27 | 1531.9 | 204.26 |
Tolerances, straightness and inspection
Square tube is checked for outside size, wall thickness, corner radius, squareness of the corners, twist and straightness. For ASTM orders the tolerance tables of ANSI H35.2 apply; for EN orders, EN 755-8 (porthole tube) or EN 755-7 (seamless). Twist is the parameter most often overlooked on long frame members: if your assembly is jig-welded, state a twist limit per metre on the drawing.
Quality checks
- Dimensions
- Outside size, wall at several points, corner radius and length on each lot
- Form
- Straightness, twist and convexity or concavity of the faces
- Mechanical
- Tensile test per lot; hardness or conductivity check on request
- Surface
- Visual check for die lines, scratches and dents, with PVC film or interleaving if specified
- Certification
- EN 10204 3.1 mill test certificate
Cutting, welding, bending and finishing square tube
Welding
TIG and MIG weld well with ER4043 or ER5356 filler. Strength near the weld drops to about T4 level, so place welds away from peak bending moment or design to welded allowables.
Bending
Square tube tends to buckle on the inside face and bow on the outside. Use a mandrel or filler, generous radii (at least 3 – 4 × the outside size in T6), or bend in T4 and age afterwards.
Machining
Machines with short chips and a good finish. Clamp thin walls with soft jaws or internal plugs to avoid crushing.
Anodising
Takes clear and coloured anodising; the finish is slightly less uniform than 6063, so choose 6063 if appearance is the priority.
Corrosion
Good in atmosphere and fresh water. In marine splash zones anodise or paint, and isolate steel fasteners to prevent galvanic corrosion.
Where 6061 square tube is used
- Machine frames and guarding: welded or bolted bases, enclosures and conveyor stands
- Transport: trailer frames, truck bodies, ramps, roof racks and EV battery-pack frames
- Marine: boat T-tops, rails, ladders and deck furniture, usually anodised
- Construction: handrails, balustrade posts, platforms, access structures and curtain-wall sub-frames
- Solar and outdoor: PV mounting frames and signage structures
- Robotics and automation: gantries, end-of-arm tooling and test rigs
- Sport and leisure: fitness equipment, go-kart chassis and stage trusses
6061 vs 6063, 6082 and 7075 square tube
| Property | 6061-T6 | 6063-T6 | 6082-T6 | 7075-T6 |
|---|---|---|---|---|
| Typical tensile | 310 MPa | 241 MPa | 310 – 340 MPa | 570 MPa |
| Typical yield | 276 MPa | 214 MPa | 260 – 310 MPa | 505 MPa |
| Surface finish / anodising | Good | Excellent | Good | Fair |
| Weldability | Good | Good | Good | Poor |
| Range of square sizes | Wide | Widest | Wide (Europe) | Limited |
| Typical use | Structural frames | Architectural, trim | Structural (EN projects) | High-stress parts |
Choose 6063 square tube when appearance matters more than load, 6082 when your project is designed to EN 1999 and European stock sizes, and 7075 only for unwelded, highly stressed parts.
How to order 6061 square tube
- SpecifyAlloy and temper (for example 6061-T6, 50 × 50 × 3 mm), section size and wall thickness, length, quantity and the governing standard (ASTM B221, B429 or EN 755-2). A drawing helps for cut parts.
- QuoteWe confirm availability, tolerances, certification and delivery terms (EXW, FOB, CIF or DAP) for your destination.
- ProcessMaterial is cut to length, de-burred and, if you ask, bent, machined or finished before packing.
- DocumentEach shipment carries a mill test certificate to EN 10204 3.1 with chemistry and tensile results, plus the packing list. Third-party inspection can be arranged.
- ShipBundled with end caps and interleaving or packed in seaworthy wooden cases, then shipped by sea or air.
References and standards
- ASTM B221 – Aluminum and Aluminum-Alloy Extruded Bars, Rods, Wire, Profiles, and Tubes
- ASTM B429/B429M – Aluminum-Alloy Extruded Structural Pipe and Tube
- EN 755-2 – Extruded rod/bar, tubes and profiles: mechanical properties (with EN 755-7 / -8 / -9 dimensional tolerances)
- The Aluminum Association – International Alloy Designations and Chemical Composition Limits (Teal Sheets)
- The Aluminum Association – Aluminum Design Manual (welded and non-welded design properties)
6061 square tube: frequently asked questions
How much does 6061 square tube weigh?
For sharp corners, weight in kg/m = 2 × (2 × side − 2 × wall) × wall × 2.70 / 1000. A 50 × 50 × 3 mm tube weighs about 1.52 kg/m and a 100 × 100 × 6 mm tube about 6.09 kg/m. Radiused corners make it slightly lighter.
Is 6061 square tube stronger than 6063?
Yes. Typical yield strength in T6 is about 276 MPa for 6061 against 214 MPa for 6063, so 6061 carries roughly 30 % more load in the same section. 6063 has the better surface finish.
Is 6061 aluminum square tubing seamless?
Most square tube is porthole-extruded and contains seam welds formed inside the die, which are sound for structural use. Seamless square tube can be supplied when pressure duty or a specification requires it; state this on the order.
Can 6061-T6 square tube be welded without losing strength?
Welding reduces strength near the joint to about 165 MPa tensile. Most welded frames are designed to this reduced value; full T6 strength returns only if the assembly is solution treated and aged again.
What is the difference between T6 and T6511 square tube?
Both have the same strength. T6511 has been stretched to relieve stresses and may receive minor straightening, which keeps machined parts more stable. For most tube orders T6 is specified.
Do you supply 6061 square tube internationally?
Yes. Metline ships from Mumbai to customers worldwide with mill certificates, export packing and EXW, FOB, CIF or DAP terms.
Need 6061 square tube?
Send size, wall, length, quantity and destination port, and we will reply with availability, certification and a delivered price.
