The clean answer to 6063 vs 6061 aluminum: 6063 is the extrusion alloy, 6061 is the strength alloy. 6063 is built to fill complex thin-wall die shapes at high speed and to anodize bright and even. 6061 is built to carry load — it is roughly 40% stronger in T6 and machines better, but it extrudes more slowly and anodizes duller.
Both are magnesium-silicon (6xxx) heat-treatable alloys, and they are the two most common extrusion grades in the world. The choice is shape and finish against strength.
The numbers
| 6063-T5 | 6061-T6 | |
|---|---|---|
| Tensile strength | ~180 MPa | ~310 MPa |
| Yield strength | ~140 MPa | ~270 MPa |
| Elongation | ~11% | ~10% |
| Extrudability | excellent — thin walls, fast | good, but slower |
| Anodizing | bright, even, color-stable | acceptable, duller |
| Machinability | fair | good |
| Relative cost | lower per profile | higher |
The strength gap is the headline: 6061-T6 is about 40% stronger than 6063-T5. But 6063 wins on the two things that decide most architectural jobs — it fills the shape and it finishes clean.
Where 6063 wins
- Architectural profiles. Windows, doors, curtain wall, handrail, louvres — anything with a thin wall or a complex cross-section. 6063 extrudes these at speed and to a consistent surface.
- Decorative anodized finish. 6063's lower copper and iron give a clearer, more color-stable film, so it is the default where a facade has to match tint across hundreds of profiles.
- Heat sinks and thin-wall electronics extrusion. Where the fin is thin and the surface must be clean.
Where 6061 wins
- Structural extrusion. Load-bearing beams, brackets, frames, trailer and rail components where the profile carries weight.
- Machined parts. 6061 machines cleanly and is the default for parts that start as bar or plate and get milled or turned.
- Anything welded that must keep strength. 6061 welds (with strength loss in the HAZ); 6063 is not normally chosen for structural welded work.
The temper question
6063 is commonly supplied T5 or T6. T5 is cooled from the press and artificially aged — the standard architectural temper. T6 is solution heat treated, quenched and aged, giving higher strength (~205–240 MPa) for when the profile carries load. When a 6063 profile has structural duty, specify T6, not T5.
6061 is normally T6 or T6511 (the stretched, stress-relieved temper for bar and rod that will be machined).
The trap: mixing them up
The most common error is specifying 6063 for a structural member because "6063 is the extrusion alloy." 6063-T5 at 140 MPa yield will not carry what 6061-T6 at 270 MPa will, and no profile wall thickening replaces that cheaply. If the member is load-bearing, it is 6061 (or 6082 in Europe).
The reverse error is specifying 6061 for a purely decorative thin-wall profile. 6061 extrudes slower, costs more, and anodizes duller — for a window frame or a trim, 6063 is the right alloy and you are paying extra for strength you are not using.
The third error is assuming the two can be freely swapped on a certificate. They are different alloys with different composition limits (6061 carries copper and chromium; 6063 does not), and a drawing naming one is not satisfied by the other.
The decision in one table
| Your profile | Choose | Temper |
|---|---|---|
| Architectural, thin-wall, decorative | 6063 | T5 / T6 |
| Heat sink, electronics | 6063 | T5 / T6 |
| Structural beam, bracket, frame | 6061 | T6 |
| Machined bar / plate | 6061 | T651 / T6511 |
| Welded structural | 6061 | T6 |
Bottom line
6063 for shape and finish, 6061 for strength and machining. The rule of thumb: if the profile is decorative or thin-walled, it is 6063; if it carries load or gets machined, it is 6061. When a 6063 profile does have to carry load, remember to specify T6.
See the 6063 and 6061 grade pages for the full property tables. If you have a profile drawing, send it over — the wall thickness and the load usually make the choice obvious.