6061 aluminium for sheet metal parts: grade, thickness and formability

A 3 mm 6061-T6 bracket drawn with a 3 mm inside radius cracks on the first bend, and the same bracket in 6061-T4 forms without complaint at that radius. Heat treatment, not the alloy, made that difference. 6061 is the aluminium that a design engineer reaches for when 5052 runs out of strength, and it is also the aluminium that most often fails at the press brake because the drawing was written in the temper the part needs in service rather than the temper it needs in forming.

6061 aluminium is a heat-treatable Al-Mg-Si alloy: 1.0% magnesium, 0.6% silicon, 0.28% copper and 0.20% chromium. Its strength comes from a precipitation cycle, so unlike 5052 it can be softened, formed and hardened again — which opens a process route that 5052 does not have, and closes a set of bend radii that 5052 allows.

This page covers the tempers a buyer will see, the thickness range that behaves as sheet rather than plate, the bend and springback numbers in T6 and T4, and what welding does to a T6 part. The alloy that 6061 usually replaces is covered in 5052 aluminium for sheet metal parts.

What 6061 aluminium gives you, by temper

The temper decides everything downstream. O is fully annealed and forms like a different material. T4 is solution treated and naturally aged, ductile enough to form and about 145 MPa yield. T6 is artificially aged to 276 MPa yield, and forms poorly. T651 is plate that has been stretched after ageing to relieve residual stress, which is what keeps a machined part flat.

The yield-to-tensile ratio in the fifth column is the best single predictor of whether a temper will bend. At 0.89 in T6 the alloy has yielded almost all of its strength reserve before fracture, so the outer fibre of a tight bend has nowhere to go. At 0.60 in T4 there is room, and at 0.44 in O there is a lot. 5052-H32 sits at 0.74, which is why it forms at half the radius of 6061-T6.

What the strength buys

At the same thickness, 3 mm 6061-T6 carries 73% more bending load than 3 mm 5052-H32, because section modulus is identical and yield strength rises from 160 to 276 MPa. Deflection is identical within 2%, since the moduli are 68.9 and 70.3 GPa.

That combination is the reason 6061 exists in a sheet metal shop. A machined bracket that is redesigned as a folded 6061-T6 part keeps its strength, loses most of its machining cost and drops weight. A 5052 part that is failing on load can move to 6061-T6 at the same gauge, if the radii allow it.

Which thickness of 6061 aluminium behaves as sheet

6061-T6 sheet is stocked from 0.5 mm to 6.0 mm; beyond that it is plate, and plate is T651 territory: cut, drilled and machined rather than folded. Ganesh cuts 6061 to 20 mm on the 12 kW fibre laser with its 40 ft × 16 ft bed and forms up to 10 mm on the 200 T 5-axis brake, so a 6061 part within that range stays in one route.

Mass per unit area is thickness × 2.70 kg/m² per mm, which is 0.02 kg/m² per mm above 5052. That difference never decides anything. What decides is that at equal stiffness 6061 needs 1.44 × the thickness of steel (68.9 GPa against 205 GPa gives a cube root of 2.98), and at equal strength 6061-T6 needs only 0.95 × the thickness of 2 mm CRCA at 250 MPa yield, because 276 MPa is above it. No other aluminium sheet temper lets a part match CRCA in bending strength at a thinner gauge.

Thickness tolerance on 6061 follows the same mill band as other sheet alloys and moves the bend deduction the same way; the method of turning it into a dimension is worked through in thickness tolerance and its effect on 5052 aluminium parts, and the arithmetic is identical.

6061 aluminium formability: why T6 cracks and T4 does not

The radius limit

For a 90° bend, 6061-T6 needs an inside radius of 2.5–3.0 × thickness. T4 needs 1.0–1.5 ×, and O about 0.5 ×. Those figures come from trials, not from the elongation column, because bend strain concentrates over a short arc and the outer fibre sees far more strain than a tensile test reports. The minimum bend radius table by material sets out where the numbers come from.

Grain direction adds about 0.5 × thickness when the bend line runs parallel to the rolling direction. A 6061-T6 bracket that forms at 2.5 × t across the grain needs 3.0 × t with the grain, and the difference is not visible on a drawing unless someone writes it there.

A worked bend deduction in 6061-T6

Take 3 mm 6061-T6, a 90° bend at a 9 mm inside radius (3 × t), K = 0.50 — high-strength aluminium at a large radius-to-thickness ratio sits close to mid-thickness:

• Bend allowance = (π/180) × 90 × (9 + 0.50 × 3) = 1.5708 × 10.5 = 16.49 mm.
• Outside setback = (9 + 3) × tan 45° = 12.00 mm.
• Bend deduction = 2 × 12.00 − 16.49 = 7.51 mm.
• Two 100 mm flanges give a flat length of 200 − 7.51 = 192.5 mm.

The same part in 5052-H32 at 3 × t has a bend deduction of 1.953 × 3 = 5.86 mm. The 6061-T6 version costs 1.65 mm of developed length per bend and 1.5 × t of extra flange before the bend even starts. A folded box in 6061-T6 therefore needs larger blanks, larger bend reliefs and more clearance to the next feature than the same box in 5052.

Springback, and what it does to the brake

Springback scales with yield strength divided by modulus: 276 ÷ 68,900 = 4.01 × 10⁻³ for 6061-T6 against 1.22 × 10⁻³ for CRCA at 250 MPa, a factor of 3.3. At the same radius-to-thickness ratio, a 90° bend in T6 springs back 6–10° where CRCA springs back 2–3°. T4 sits at 145 ÷ 68,900 = 2.10 × 10⁻³, so it behaves closer to 5052-H32 at 3–5°.

The correction lives in the brake program, and the Delem control on the 200 T machine stores it per bend. What it cannot store is the direction of the coil. A part nested with the grain in one batch and across it in the next springs back differently, so the nesting orientation belongs in the setup sheet, not in the operator's judgement.

Welding 6061 and the heat-affected zone

6061-T6 welds with 4043 or 5356 filler. 5356 gives a stronger joint and a closer colour match after anodising; 4043 is more tolerant of fit-up and less prone to hot cracking on thick sections. On a visible anodised frame, the filler choice shows as a colour difference that no amount of finishing removes.

The heat-affected zone is the design limit. Welding takes the parent metal beside the bead back through the ageing temperature, and the zone recovers only 55–65% of parent strength. A joint in 6061-T6 is therefore designed at about 165 MPa, not 310 MPa. A post-weld age at 175 °C for several hours recovers part of the loss, and it also distorts the part, so it has to be planned with a fixture and a machining allowance rather than added at the end.

Ganesh does not run a solution treatment or ageing furnace. Where a drawing calls for a T4 forming route followed by ageing, the heat treatment is a specialist process outside our scope and the part is quoted with that step identified. The rest of the welding behaviour — travel speed, filler, distortion and the 5–8 mm bow on a free 900 mm seam — is covered in welding aluminium sheet assemblies.

Coating and anodising 6061

6061 anodises to a brighter, cleaner clear film than 5052, which is why visible trim and architectural parts in aluminium are usually 6061 or a 5xxx grade chosen for colour. Type II anodising at 10–25 µm works well; hard anodising at 25–50 µm is used on wear surfaces.

Powder coating is the constraint. Polyester cures at 180–200 °C metal temperature, and artificial ageing of 6061 starts near 175 °C. Above 190 °C the temper overages and yield strength falls, and the loss does not come back at room temperature. Set the oven for the heaviest part in the load, record the profile, and rack similar masses together. The chemistry on the pretreatment line is the aluminium cycle, not the steel one, and the reason is set out in 5052 aluminium corrosion and finish compatibility.

Cut edges matter here too. A laser-cut 6061 edge carries a remelt layer, and an anodised edge shows it as a dark line because the film forms differently on the recast. Where the edge is visible, specify deburring or a machined edge rather than expecting the anodiser to hide it.

6061 aluminium on the Ganesh route

6061 is cut on the 12 kW fibre laser with the 40 ft × 16 ft bed, formed on the 200 T 5-axis CNC brake with a 4,450 mm bed to 10 mm, and welded in three CLOOS robotic MIG cells or at the 30-plus manual stations, with fixtures built in our own tool room. The same plants run copper, brass and aluminium work through copper, brass and aluminium fabrication, so a non-ferrous part does not need a separate supplier.

Typical sheet metal tolerance is ±0.5 mm, tighter on critical features by agreement; PPAP and first article inspection are available; both plants hold ISO 9001:2015 and ISO 14001:2015. Aluminium parts in the custom parts range run 0.8–40 mm, which covers 6061 sheet and plate in the same route as the steel work. The materials and grades hub holds the grade-selection pages for the other alloys.

What to put on the drawing

1. Alloy and temper by designation — "6061-T6" or "6061-T4", never "aluminium".
2. The forming route, if it is T4 and age afterwards, with the ageing specification and who runs it.
3. Inside radius on every bend, plus the grain direction requirement for the tight ones.
4. Bend relief and hole-to-bend distances, sized for the larger radius a T6 part needs.
5. Weld symbols, filler alloy and the design stress assumed in the heat-affected zone.
6. Cure or service temperature limit, expressed as a maximum metal temperature.
7. Anodising type, film thickness and the faces that must stay conductive.
8. Flatness and twist limits after forming and after any heat treatment.

Ordinary dimensions default to ISO 2768-1 where the drawing does not call out individual tolerances, which covers linear and angular dimensions but says nothing about bend angle, springback or flatness. Those need notes of their own.

When 6061 is the wrong choice

6061-T6 is the wrong alloy when the part is defined by tight bends, by stiffness, or by cost. Under 1.5 × thickness radius it will not form in T6, and a T4 route adds a heat treatment step and a distortion risk. Where deflection rather than stress controls the section, the 68.9 GPa modulus means steel at 0.7 × the thickness does the same job for less. And where 5052 at the correct gauge already carries the load, 6061 adds cost without adding anything to the part.

We cut and form 6061 to 10 mm formed and 20 mm cut. Above that, or where the drawing needs solution treatment and ageing in-house, we will say so before quoting rather than after.

Send the revision with the temper, radii and quantity through request a quote, and the review will state the forming route and the flat pattern basis it assumes.