Temper Is Part of the Alloy Spec
When a drawing says 6063-T5 or 6063-T6, the temper is as important as the alloy. T5 and T6 are heat-treatment states that change the strength, hardness and cost of the profile. Many first-time buyers focus on the alloy number and miss the temper – then wonder why the part flexes or strips threads. The temper is a decision, not an afterthought, and it should be fixed on the drawing before the die is even made.
T5: Cooled, Aged, Ready
T5 starts with air cooling after extrusion, followed by artificial ageing in an oven. The result is a solid middle-ground temper: 6063-T5 typically delivers around 150-160 MPa tensile strength, good enough for frames, rails, trims and most architectural and industrial profiles. T5 is the lower-cost option because it skips the quenching step, and for parts that do not carry heavy load it is the economical default.
T6: Quenched and Aged Harder
T6 adds a water-quench step right at the press exit, then the same artificial ageing. The quench locks the alloying elements in solution, and the ageing precipitates them for maximum strength. 6063-T6 reaches roughly 205-240 MPa – about 40 percent stronger than T5. Use T6 where profiles carry load, hold threaded inserts, or act as structural members in heat sinks and equipment frames. The trade-off is slightly higher cost and tighter process control.
How to Choose T5 or T6
A simple rule: if the profile carries weight, resists bending, or takes screws, choose T6. If it is decorative, architectural or lightly loaded, T5 keeps cost down. The same die can run both tempers, so changing later only affects price and lead time. When in doubt, ask the extruder for the hardness spec: 8-12 HW for T5, 12-14 HW for T6, measured with a Webster tester. Siken Aluminum quotes both tempers with hardness reports on every order.
Frequently Asked Questions
What is the difference between T5 and T6 temper?
Both are heat-treated tempers of 6xxx aluminium. T5 is cooled from the extrusion press and artificially aged without a separate solution treatment, while T6 goes through solution heat treatment, quenching and artificial ageing. T6 typically delivers higher strength (for example 6063-T6 about 240 MPa tensile vs T5 about 205 MPa).
When should I specify T6 instead of T5?
Choose T6 for structural frames, high-load heat sink bases and parts that need maximum mechanical strength. T5 is often preferred for thin-wall or complex fin geometries where the quench of T6 could distort the section.
Does heat treatment affect profile straightness or tolerance?
It can. The quench step in T6 can introduce slight distortion on long, thin profiles. We control stretching and straightening after treatment and can measure straightness/twist to standard tolerances before delivery.