6063 vs 6061 aluminium in window profiles
Window profiles are extruded 6063: it extrudes the complex multi-chamber section cleanly, takes the anodise and powder finish, and carries the wind load the frame is sized for. 6061 is the stronger, more machinable alloy — roughly 2.5 times the yield strength of 6063 in the T6 condition — and it shows up on the window at the hardware and the reinforcement: the bearing that carries a 400 kg pivot leaf, the stiffener behind a 4,000 mm fixed pane. The frame wants 6063; the load points want 6061. The specification names both.
What the alloy number is doing
Both are magnesium-silicon alloys, which is why both form the hard, wear-resistant magnesium silicide phase — but in different proportions. 6063 keeps the balance on the extrusion side: it flows through the die as a complex thermal-break section, it holds the tight tolerances the gasket channel needs, and it finishes clean for the anodise bath or the powder line. 6061 pushes the silicon higher, which buys the yield strength after T6 tempering and the machinability — the alloy of the structural member, the machined part and the welded sub-assembly.
Why 6063 is the frame alloy
The strength a window frame needs comes from the section — the chamber count, the wall thickness, the reinforcement — not from the alloy yield. The wind load is carried by geometry, and 6063 at the T5 temper is more than enough for the profile, with the finish behaviour that 6061 does not match: the extruded surface takes the anodise even and the powder coat without the surface chemistry problems that show as streaks on the façade. Pushing 6061 through a multi-chamber thermal-break die is the wrong trade — more die wear, worse finish, and strength the section was not going to use.
On the data sheet the profile line reads 6063 with the temper stated. The question to ask a supplier is the temper and the finish specification, not a higher alloy number for the frame.
Where 6061 shows up on the window
- The bearings: the PV-75 pivot carries 400 kg on floor and head bearings — machined 6061 is the standard material for the load point.
- The reinforcement: behind the large fixed lites, the structural stiffener takes the glass load, and the 6061 plate is the common answer on the shop drawing.
- The hardware engagement: the multi-point striker plates and the hinge hardware on the heavy sashes — machined, not extruded.
- The structural sub-assemblies: the corner build on the panoramic line and the threshold housing on the barrier-free detail, where the member is machined or welded rather than extruded.
How it reads on the schedule
A complete schedule carries the alloy in three lines: the profile (6063, temper stated), the reinforcement and load points (6061-T6 or the steel equivalent, named per position), and the hardware (the stainless or alloy schedule the finish column already sets). The price follows the geometry and the hardware, and a frame quoted in 6061 is usually a specification error, not an upgrade — the visible performance on the façade does not move with the alloy number on the profile line.
Questions
Not for the profile — the frame strength comes from the section, and 6063 finishes cleaner. 6061 is the right alloy at the bearings, the reinforcement and the machined hardware.