What Is an Extrusion Temper and Why It Matters

What Does Extrusion Temper Mean in Practice

Extrusion temper is the mechanical condition of the metal after it leaves the extrusion die and passes through a controlled heat treatment. The alloy determines what the metal can do. The temper determines how well it does it.

An extrusion profile made from 6061 alloy in the O temper is soft and easy to cut. The same alloy in T6 temper is stronger and stiffer. The chemistry is the same. The crystal structure and internal stress are different. That difference changes the profile under load.

When a buyer asks for a specific alloy, the second question is always the temper. The alloy tells you the composition. The temper tells you the performance.

How Heat Treatment Creates the Temper

Heat treatment is the process that changes the extrusion temper. It usually involves three steps: solution treatment, quenching, and aging.

The extrusion is first heated to a high temperature where the alloying elements dissolve into the aluminum matrix. The metal becomes a single phase. It is soft.

The hot metal is then cooled rapidly, usually by water quenching. This traps the alloying elements in solid solution. The structure is unstable. It holds energy but not yet strength.

The final step is aging. The profile is held at a lower temperature. The alloying elements precipitate out of the matrix in small particles. These particles block dislocation movement. The metal becomes harder and stronger.

The length and temperature of the aging step set the final temper. Longer aging usually means higher strength but slightly lower ductility.

Annealed vs T6 and How They Differ

The most common comparison in extrusion buying is between annealed and T6 temper. The difference is not cosmetic.

Annealed metal, often marked O or O1, is soft. The grain structure is relaxed. It is easy to machine, bend, and stamp. It is used for decorative profiles, low-stress parts, and applications where the profile will be bent or formed after extrusion.

T6 temper is a thermally stabilized condition. It is the standard for structural and load-bearing extrusions. T6 has higher yield strength and higher stiffness. It holds its shape better under load. It is harder to machine and harder to bend.

The choice is not about which is better. It is about which fits the part. A sign structure may need T6 to span a distance without sagging. A decorative trim piece may need O temper to allow a 90 degree bend without cracking.

What the Temper Code Tells You

Temper codes follow a standard system. The letter indicates the process. The number indicates the condition after that process.

O means annealed or fully recrystallized. The metal has been heated and cooled slowly. It is soft and workable.

T4 means solution treated and naturally aged. The metal has been quenched and left to age at room temperature. It is stronger than O but weaker than T6. It is often used for architectural aluminum where moderate strength and good corrosion resistance are needed.

T6 means solution treated and artificially aged. The metal has been heated after quenching to promote precipitation. It is the strongest of the common extrusion tempers.

T73 and T74 are stress-relieved or overaged conditions. They are used when a part will undergo further fabrication, such as welding or machining, after the initial heat treatment. They reduce the risk of cracking during subsequent heat cycles.

The code is a specification. It tells the manufacturer what to do and what the buyer expects to receive.

How Temper Changes Physical and Chemical Properties

Temper changes the properties that matter on the shop floor and in the field.

Strength: T6 extrusions have higher yield strength than O extrusions. This means they resist deformation under load. A T6 beam will deflect less than an O beam of the same size and alloy.

Stiffness: Modulus of elasticity is a material property that does not change much with temper. However, the ability to carry load without yielding is much higher in T6. This matters for long spans.

Corrosion resistance: Temper does not change the corrosion resistance of the alloy itself. 6061 in O and 6063 in T6 both corrode at similar rates in the same environment. The alloy controls corrosion. The temper controls strength.

Workability: O temper is easier to cut, drill, and bend. T6 is harder. Cutting T6 produces more heat and wears tooling faster. Bending T6 requires more force and a smaller radius.

A Worked Example: A Structural Frame vs a Decorative Trim

Consider a buyer sourcing two items from the same extrusion mill. The first item is a vertical support for a commercial storefront. The second item is a horizontal trim piece for the same storefront.

The support must carry the weight of the structure and resist wind load. It must not bend. It must hold its shape for the life of the building. The buyer specifies a structural alloy in T6 temper. The mill heats the profile to solution treatment temperature, quenches it, and ages it at a controlled temperature. The result is a stiff, strong profile that resists deformation.

The trim piece is decorative. It must be formed into a 90 degree corner. It must be easy to machine for end caps. The buyer specifies the same alloy in O temper. The mill anneals the profile. The result is a soft profile that can be bent without cracking and machined with standard tools.

The alloy is the same. The temper is different. The final parts are different.

How to Match Temper to Sourcing Decisions

When writing a purchase order, specify both the alloy and the temper. Do not leave it to the mill to guess.

Start with the load. If the part carries structural load, ask whether O temper is enough. In most structural applications, the answer is no. You need T6 or a comparable high-strength temper.

Next, consider fabrication. If the part will be welded, drilled, or bent after extrusion, check whether the temper will survive the process. High-strength tempers can crack if the welding heat affects too wide a zone. A T73 temper may be chosen to reduce that risk.

Check the corrosion environment. The temper will not save you from corrosion. Choose the right alloy for the environment. Then choose the temper for the mechanical requirements.

Finally, check the tolerances. Heat treatment changes the metal. It can cause slight dimensional shifts. If your part has tight tolerances, confirm with the mill how they control the shift. Some mills use stress relief steps to minimize this.

Temper	Typical Process	Strength	Workability	Common Use
O	Annealed	Low	High	Bending, stamping, decorative parts
T4	Solution treated, natural aging	Moderate	Moderate	Architectural profiles, low stress
T6	Solution treated, artificial aging	High	Low	Structural profiles, load bearing
T73	Solution treated, artificial aging, stress relief	High	Moderate	Welded or machined parts
T8	Solution treated, artificial aging	Very High	Very Low	High strength aerospace or specialty

Common Mistakes in Temper Selection

The most common mistake is specifying only the alloy. The buyer writes 6061. The mill ships T6. The buyer finds the part too hard to bend. The mill shipped the wrong temper for the application.

Another mistake is assuming T6 is always stronger. T6 is strong, but it is not the strongest temper for every alloy. Some alloys can reach higher strength in different aging conditions. The alloy and temper must be chosen together.

A third mistake is ignoring the downstream process. A buyer orders T6 for a part that will be welded. The welding heat softens the metal around the joint. The part fails at the weld. A T73 temper would have been a better choice.

A fourth mistake is not checking the mill s heat treatment records. For critical parts, request the heat treatment log. It shows the solution treatment temperature, quench time, and aging temperature. This is the proof that the temper is as specified.

Final Checks Before Ordering

Before placing an order, run three checks.

1. Confirm the alloy and temper in the drawing or specification. Write them clearly. Do not use abbreviations that can be misread.
2. Confirm the heat treatment method. Ask the mill how they achieve the specified temper. Ask for the heat treatment records.
3. Confirm the downstream process. If the part will be bent, welded, or machined, tell the mill. Ask whether the chosen temper will survive.

The extrusion temper is not a footnote. It is the difference between a part that works and a part that fails. Match the alloy to the corrosion and strength needs. Match the temper to the load and fabrication needs. That is how you source extruded aluminum that performs as designed.