O
Annealed, soft. For severe bending; heat-treat to T6 afterwards to recover strength.
Marine bar stock
6061 Marine Aluminium Square Bar for Shipbuilding
6061 square bar is the general-engineering aluminium bar of the Americas and Asia: heat-treatable, strong in T6, easy to machine and weld, and a class-recognised extrusion alloy for ships. On vessels it is used for brackets, stiffeners, machinery foundations, hatch frames and machined blocks above the waterline. Metline supplies 6061 square bar in O, T4, T6 and stretched tempers, certified to ASTM, EN or GB standards, worldwide.
- Alloy
- 6061 (Al-Mg-Si-Cu)
- Tempers
- O, T4, T6, T3511, T6511, T8511
- Side length
- about 10 – 150 mm
- Standards
- ASTM B221 · EN 755-2 · GB/T 3191
6061 square bar on ships and boats
6061 has been the default heat-treatable aluminium for general engineering since the 1930s. Its magnesium and silicon form the Mg2Si strengthening phase, a little copper adds strength and chromium controls grain structure and stress-corrosion resistance. In T6 temper extruded bar it delivers at least 260 MPa tensile and 240 MPa proof strength under EN 755-2, with typical values near 310 and 275 MPa.
In marine work 6061 is one of the extrusion alloys listed by class societies, together with 6005A and 6082. It is used for welded secondary structure, machinery seats, brackets, frames for hatches and doors, and as stock for machined parts. Square bar is particularly handy because its flat faces give clean datum surfaces for milling and solid stock for weld-on lugs and pads.
Two cautions apply. First, the copper content (0.15 – 0.40 %) makes 6061 slightly less resistant to pitting in seawater than 5xxx alloys or low-copper 6082, so parts below the waterline should be anodised, painted or replaced by a 5xxx grade. Second, welding softens the heat-affected zone to roughly T4 level, so welded joints must be designed with reduced allowable stresses.
6061 chemical composition (wt %)
| Element | 6061 |
|---|---|
| Silicon (Si) | 0.40 – 0.80 |
| Iron (Fe) | ≤ 0.70 |
| Copper (Cu) | 0.15 – 0.40 |
| Manganese (Mn) | ≤ 0.15 |
| Magnesium (Mg) | 0.80 – 1.20 |
| Chromium (Cr) | 0.04 – 0.35 |
| Zinc (Zn) | ≤ 0.25 |
| Titanium (Ti) | ≤ 0.15 |
| Others, each / total | ≤ 0.05 / ≤ 0.15 |
| Aluminium (Al) | Remainder |
These limits are common to ASTM B221, EN 573-3 (EN AW-6061, AlMg1SiCu) and GB/T 3190. The actual analysis of each cast is reported on the mill certificate.
Mechanical properties by temper
| Alloy-temper | Size D (mm) | Tensile Rm (min) | Proof Rp0.2 (min) | Elongation A |
|---|---|---|---|---|
| 6061-O | ≤ 200 | ≤ 150 MPa | ≤ 110 MPa | ≥ 16 % |
| 6061-T4 | ≤ 200 | 180 MPa | 110 MPa | ≥ 15 % |
| 6061-T6 | ≤ 200 | 260 MPa | 240 MPa | ≥ 8 % |
| Temper / standard | Tensile (min) | Yield (min) | Elongation |
|---|---|---|---|
| T6 / T6511 extruded, ASTM B221 | 260 MPa (38 ksi) | 240 MPa (35 ksi) | 8 – 10 % |
| T6 cold-finished, ASTM B211 | 290 MPa (42 ksi) | 240 MPa (35 ksi) | 10 % |
| T6, typical | about 310 MPa | about 275 MPa | 12 % |
In GB/T 3191, T3511 carries the same minimums as T4, and T8511 the same as T6; the suffixes indicate stretching (and, for T8, cold work before ageing) to relieve residual stress and improve straightness.
Physical properties (T6)
- Density
- 2.70 g/cm³
- Elastic modulus
- 68.9 GPa
- Thermal conductivity
- 167 W/m·K
- Electrical conductivity
- 43 % IACS
- Coefficient of thermal expansion
- 23.6 µm/m·°C
- Melting range
- 582 – 652 °C
Which temper to order
T4 / T3511
Solution treated and naturally aged (T3511 also stretched). Formable, then age to T6.
T6
Full strength, standard for machining and structure.
T6511 / T8511
Stretched full-strength bar with low residual stress, preferred for precision milling.
Standards and equivalents
| System | Designation | Bar standard |
|---|---|---|
| USA | 6061 / UNS A96061 | ASTM B221, B211; AMS-QQ-A-200/8 |
| Europe | EN AW-6061 / AlMg1SiCu (3.3211) | EN 755-2, EN 754-2 |
| Japan | A6061 | JIS H4040 |
| India | 65032 | IS 733 |
| China | 6061 (formerly LD30) | GB/T 3191 |
Sizes and weights
Supply range
- Side length
- About 10 – 150 mm; metric and imperial (3/8 – 6 in) sizes
- Length
- 3 – 6 m or 12 ft; cut-to-length pieces
- Finish
- Mill, anodised; precision-milled blocks on request
| Side (mm) | kg per metre | kg per 3 m bar | kg per 6 m bar |
|---|---|---|---|
| 10 | 0.270 | 0.81 | 1.6 |
| 12 | 0.389 | 1.17 | 2.3 |
| 16 | 0.691 | 2.07 | 4.1 |
| 20 | 1.08 | 3.24 | 6.5 |
| 25 | 1.69 | 5.06 | 10.1 |
| 30 | 2.43 | 7.29 | 14.6 |
| 40 | 4.32 | 12.96 | 25.9 |
| 50 | 6.75 | 20.25 | 40.5 |
| 60 | 9.72 | 29.16 | 58.3 |
| 75 | 15.19 | 45.56 | 91.1 |
| 80 | 17.28 | 51.84 | 103.7 |
| 100 | 27.00 | 81.00 | 162.0 |
| 120 | 38.88 | 116.64 | 233.3 |
| 150 | 60.75 | 182.25 | 364.5 |
Tolerances
Extruded 6061 square bar is normally supplied to ANSI H35.2 (for ASTM orders) or EN 755-4 / GB/T 14846. Typical side-length tolerances for EN orders:
| Side length (mm) | Tolerance (mm) |
|---|---|
| over 18 to 25 | ±0.25 |
| over 25 to 40 | ±0.30 |
| over 40 to 50 | ±0.35 |
| over 50 to 65 | ±0.40 |
| over 65 to 80 | ±0.45 |
| over 80 to 100 | ±0.55 |
| over 100 to 120 | ±0.65 |
| over 120 to 150 | ±0.80 |
Cold-finished bar to ASTM B211 holds tighter size tolerances and sharper corners, useful for keys and slide parts.
Machining, welding and protection
Machining
Very good in T6: short chips, bright finish. Use carbide, high speeds and coolant.
Welding
MIG/TIG with ER5356 for marine structures, ER4043 for crack-sensitive joints. HAZ strength falls to roughly 165 MPa tensile (as-welded design value commonly used).
Bending
Bend radii of about 1.5 – 3 × thickness in T6; tighter in O or T4.
Corrosion protection
Anodise or paint for marine exposure; isolate from stainless and bronze; avoid copper antifouling contact.
Marine applications
- Machinery foundations and equipment seats in engine rooms
- Brackets and lugs welded or bolted to aluminium structure
- Hatch and door frames in superstructures
- Deck hardware such as cleat bases, chocks and fairlead bodies
- Ladders and gangway components
- Machined blocks for steering gear, winch parts and davits
6061 versus 6082 and 5083 square bar
| Property | 6061-T6 | 6082-T6 | 5083-H112 |
|---|---|---|---|
| Min. proof strength (bar) | 240 MPa | 250 – 260 MPa | about 110 – 125 MPa |
| Machinability | Very good | Very good | Fair |
| Seawater immersion | Fair, protect | Fair–good, protect | Excellent |
| Strength after welding | Falls to about T4 level | Falls to about T4 level | Little change |
See our 6061 vs 6082 guide for a fuller comparison.
Ordering
- SpecifyTemper, side length, length, quantity and standard (ASTM B221, EN 755-2 or GB/T 3191).
- QuoteAvailability, certificate and terms (EXW, FOB, CIF or DAP).
- PrepareCutting, marking and inspection; anodising or machining if required.
- ShipEN 10204 3.1 certificate; export packing.
References and standards
- ASTM B221 – Aluminum and Aluminum-Alloy Extruded Bars, Rods, Wire, Profiles, and Tubes
- ASTM B211 – Aluminum and Aluminum-Alloy Rolled or Cold Finished Bar, Rod, and Wire
- EN 755-2 – Extruded rod/bar, tube and profiles: mechanical properties
- ASM International – Properties of Wrought Aluminum and Aluminum Alloys: 6061
- The Aluminum Association – International Alloy Designations and Chemical Composition Limits
6061 marine aluminium (aluminum) square bar: FAQs
Is 6061 square bar good for marine use?
Yes above the waterline and in protected positions, especially anodised. For constant seawater immersion, a 5xxx alloy such as 5083 is better.
What is the difference between 6061-T6 and T6511?
Same strength; T6511 is stretched to relieve stress and lightly straightened, so it moves less when machined.
What filler should I use to weld 6061 on a boat?
ER5356 is preferred for marine structures and anodised parts; ER4043 resists hot cracking on restrained joints.
How much does a 50 mm 6061 square bar weigh?
About 6.75 kg per metre.
What are T3511 and T8511?
Stretched variants: T3511 has T4-level strength, T8511 has T6-level strength with cold work before ageing. Both offer lower residual stress.
Need 6061 square bar?
Send temper, size, length, quantity and destination for availability, certification and a delivered price.
