Aluminium Guide · Lesson 04

Aluminium tempers: what T4, T5 and T6 mean

The same alloy can be soft or hard depending on the heat treatment it received. That is the temper, and it is written after the alloy number.

4 minutes’ read

In short

The temper tells you what heat treatment the profile received; it is written after the alloy: 6063-T5.
T5: cooled at the press exit and aged in an oven. It is the standard for aluminium joinery.
T6: solution heat-treated and aged to maximum strength. T4: the softest condition, for bending or curving.

Why aluminium is "tempered"

6000-series alloys gain strength when magnesium and silicon form microscopic particles inside the metal. This is controlled with temperature and time: first these elements are dissolved at high temperature, then the metal is cooled quickly to "freeze" them, and finally it is heated for a few hours at a moderate temperature so that they precipitate. That last step is called ageing.

The most common tempers

Temper	Process	When to use it
F	As it leaves the press, with no control of properties	Hardly used in finished profiles
T4	Solution heat-treated and naturally aged at room temperature	When the part will be bent, curved or formed
T5	Cooled at the press exit and aged in an oven	Windows, doors and joinery: the standard
T6	Solution heat-treated and aged in an oven to maximum strength	Structural and machined parts

In practice, a 6063 profile leaves the press already solution-treated by the heat of the extrusion itself. If it is cooled rapidly and fully aged, it reaches T6 properties; if the cooling is gentler, it ends up in T5.

What to check when ordering

Always order alloy and temper together: "6063-T5" says much more than "6063".
If you are going to bend the profile, ask about T4: in T6 it may crack.
Welding a T6 profile lowers its strength near the weld: this is taken into account in the design calculations.

Frequently asked questions

What does T5 mean in aluminium?

That the profile was cooled at the press exit and then aged in an oven. It is the usual temper for windows and doors.

Which is stronger, T5 or T6?

T6. For example, 6063 has a minimum tensile strength of 175 MPa in T5 and 215 MPa in T6 (EN 755-2, small wall thicknesses).