T5 means the profile is cooled straight from the extrusion press and then artificially aged; T6 means it is fully solution heat treated, quenched and then aged, which gives higher strength. For 6063, T5 suits most windows and doors; T6 is used where more strength is needed. 6061 is almost always used in T6.
| T5 | T6 | |
|---|---|---|
| Process | Press-quenched, then artificially aged | Solution heat treated, quenched, artificially aged |
| Strength | Lower | Higher |
| Cost | Lower | Higher |
| Typical use | 6063 windows, doors, decoration | 6061 structural; 6063 where extra strength is needed |
Why temper matters
The same alloy can differ a lot in strength depending on temper, so a drawing should always state both, for example 6063-T5 or 6061-T6.
Questions
Which temper for curtain wall?
6063-T6 is common for curtain wall mullions where spans are long; check the structural calculation.
Can you supply T4?
Ask with the application; most extrusion orders are T5 or T6.