A6061 aluminium is the plate grade machine shops, fixture makers and equipment builders ask about most. Yet the same name "6061" can arrive as T6 or T651, a few millimetres or several centimetres thick, and each choice behaves very differently on a milling machine or under a welding torch. Rather than repeating every property of 6061, this article focuses on three buyer questions: T6 or T651, how to read the properties on a certificate, and which mistakes spoil an order.

Key properties of A6061 aluminium (compiled by H&D Steel)

A6061, 6061 and AlMg1SiCu are the same alloy

The leading "A" follows the Japanese JIS convention, common on material from Japan, Korea and China. The Aluminum Association and ASTM write 6061; Europe uses EN AW-6061, and the chemical-symbol name is AlMg1SiCu. The alloy was registered in 1954 and belongs to the heat-treatable 6xxx (Al–Mg–Si) family.

Composition limits from the Aluminum Association registration record (Teal Sheets), cross-checked against the Aircraft Materials datasheet:

Density is 2.70 g/cm³: plate weight in kilograms equals length × width × thickness in metres multiplied by 2,700.

How T6 and T651 differ

• T6: solution heat-treated, then artificially aged.
• T651: after quenching, the plate is stretched under control to relieve residual stress before artificial ageing. The aerospace specification SAE AMS4053 for 6061-T651 plate carries "stress-relief stretched" in its title.

Residual stress forms when the plate is quenched. It matters little for thin sheet that is bent or punched, but in thick plate with deep pockets or one face milled away, uneven stress release makes the part bow once unclamped. Shop practice is therefore simple: order T651 for fixtures, moulds and machine base plates that will be heavily milled; T6 is fine for thin parts, enclosures and brackets with little machining.

Properties to check on the certificate

Minimum values for 6061-T6 in the Aircraft Materials datasheet:

• 0.5–12.7 mm: tensile strength 42 ksi (about 290 MPa), yield 35 ksi (about 240 MPa), elongation 10%.
• Thicker plate: yield stays at 35 ksi while minimum elongation falls to 8% at 25–50 mm and 6% at 50–150 mm; at 100–150 mm minimum tensile strength drops to 40 ksi (about 276 MPa).

Typical values are higher: the Protolabs CNC material sheet lists 310 MPa tensile, 276 MPa yield and about 95 HB, and ESAB also gives 45 ksi typical tensile strength. Compare test results with the minimum for the correct thickness range, not with typical figures.

Welding 6061-T6: the weld is weaker than the plate

Welding heat undoes part of the heat treatment in the zone next to the weld. According to ESAB, 6061-T6 has about 45 ksi typical tensile strength before welding, while the AWS D1.2 structural code requires only 24 ksi (about 165 MPa) from a welded test piece, under 60% of the parent plate. Test bars usually break in the heat-affected zone, and higher heat input means lower strength. Welded load-bearing structures must be designed on weld-zone strength. If a part is mostly bent and welded, consider 5052 instead; see our 5052 vs 6061 comparison (Vietnamese).

Choosing thickness by process

Milling a deep pocket in thick aluminium plate — AI-generated illustration

• CNC milling: order plate thicker than the finished part to allow facing on both sides; the allowance depends on flatness requirements and clamping. Use T651 for fixture plate.
• Round parts, shafts, bushes: use 6061-T6 round bar instead of cutting from thick plate.
• Bending: 6061-T6 is hard, so it needs a larger bend radius than 3xxx or 5xxx alloys. Bend a test piece first.

Five common mistakes when buying A6061

1. Ordering "6061" without stating the temper.
2. Choosing T6 for thick plate that will be deeply milled.
3. Accepting a certificate that shows chemistry only, without tensile, yield, elongation and the standard (for example ASTM B209 or JIS H 4000).
4. Not agreeing thickness and flatness tolerances; JIS H 4000 has dedicated clauses on both.
5. Designing welded structures with parent-plate strength instead of the roughly 24 ksi weld value required by AWS D1.2.

See other grades on our aluminium plate page or read the 6061-T6 overview (Vietnamese).

References

• The Aluminum Association – Teal Sheets
• ASTM B209 – Aluminum and Aluminum-Alloy Sheet and Plate
• JIS H 4000:2022 – Aluminium and aluminium alloy sheets, strips and plates
• ESAB – Passing the tensile test with 6061-T6
• Aircraft Materials – Aluminium Alloy 6061
• Protolabs – CNC material data sheet, Aluminum 6061-T651/T6
• SAE AMS4053 – 6061-T651 plate, stress-relief stretched
• Righton Blackburns – Aluminium temper designations

Need A6061 plate or round bar for fixtures, moulds or machine frames? Send your specification (alloy, temper, thickness × width × length, quantity) to H&D Steel via hotline/Zalo 0904 678 236 (Sales Department), or request a quote on our aluminium coil and plate quotation page.