Making Sense of Aluminum Extrusion Tempers

Aluminum BilletsWhen considering the use of extruded aluminum to solve a design problem, you should be familiar with aluminum alloys and tempers. Aluminum alloys are identified primarily by a series number— a four-digit code describing its metallurgical composition. For extruded aluminum, the most common series are 6000’s and 7000’s.

The 6000 (Al-Mg-Si) series is the most popular alloy given that it doesn’t work-harden quickly. This means it can be more easily extruded and profiles manufactured more cost-effectively. The 7000 series has a significant amount of zinc which makes it the strongest alloy and popular for marine, automotive and aviation applications, but takes higher forces to extrude.

While the alloys themselves do offer certain levels of strength, based on the secondary mineral or compound added to the aluminum, that alone should not be the basis for selecting one over another. Depending on the composition of your alloy, aluminum can be further strengthened and hardened using quenching (cooling), heat treatment, and/or cold working techniques. This is called the temper and appears as a hyphenated suffix to the basic alloy number, such as 6061-T1.

How Tempers Impact Your Product

Each of these techniques can enable designers to achieve desired mechanical properties using a more easily extruded, less expensive alloy. For example, alloy 6063, typically a good match for decorative purposes, offers an attractive surface finish and can be used to extrude thin walls or fine details. Un-heat-treated 6063 has an ultimate strength no more than 19,000 psi and no specified maximum yield strength. At first glance, its use seems limited given its low strength. However, when T6 tempered (6063-T6) its minimum ultimate strength becomes 30,000 psi and its minimum yield 25,000 psi. This increase in strength created with a combination of solution heat treatment and artificial aging makes the alloy useful for architectural applications, particularly window and door frames.

The temper of each alloy can also create considerable variances in their characteristics and how they react to various fabrication processes, such as punching, forming and welding. Understanding these designations ensures you don’t destroy key capabilities. For example, you can improve the corrosion resistance of certain alloys by choosing an appropriate solution heat treatment, a suitable quench rate, and age-process sequence, at the expense of strength. And vice versa.

Basic Temper Designations

The first designation, which is a letter (F, H, O, T or W), indicates the general class of treatment. The first digit after the letter indicates a basic operation. For example, 6060-T4 indicates the use of 6060 alloy and a T4 temper, which means the extrusion is thermally treated (T) after being extruded and then naturally aged (4).

F As fabricated – Applies to products of a forming process in which no special control over thermal or strain hardening conditions is employed
O Annealed – Applies to a product which has been heated to produce the lowest strength condition to improve ductility and dimensional stability
H Strain Hardened – Applies to products which are strengthened through cold-working. The strain hardening may be followed by supplementary thermal treatment, which produces some reduction in strength. The “H” is always followed by two or more digits.
W Solution Heat-Treated – An unstable temper applicable only to alloys which age spontaneously at room temperature after solution heat-treatment
T Thermally Treated – To produce stable tempers other than F, O, or H. Applies to a product which has been heat-treated, sometimes with supplementary strain-hardening, to produce a stable temper. The “T” is always followed by one or more digits.

Further to the basic temper designation, there are two subdivision categories to the “H” Temper (Strain Hardened) and “T” Temper (Thermally Treated) categories.

Subdivisions of H Temper – Strain Hardened

The first digit after the H indicates a basic operation: The second digit after the H indicates the degree of strain hardening:
H1 – Strain Hardened Only HX2 – Quarter Hard
H2 – Strain Hardened and Partially Annealed HX4 – Half Hard
H3 – Strain Hardened and Stabilized HX6 – Three-Quarters Hard
H4 – Strain Hardened and Lacquered or Painted HX8 – Full Hard
HX9 – Extra Hard

Subdivisions of T Temper – Thermally Treated

The first digit after the T indicates a basic operation:
T1 – Naturally aged after cooling from an elevated temperature shaping process, such as extruding.
T2 – Cold-worked after cooling from an elevated temperature shaping process and then naturally aged.
T3 – Solution heat-treated, cold-worked and naturally aged.
T4 – Solution heat-treated and naturally aged.
T5 – Artificially aged after cooling from an elevated temperature shaping process.
T6 – Solution heat-treated and artificially aged.
T7 – Solution heat-treated and stabilized (overaged).
T8 – Solution heat-treated, cold-worked and artificially aged.
T9 – Solution heat-treated, artificially aged and cold-worked.
T10 – Cold-worked after cooling from an elevated temperature shaping process and then artificially aged.
Additional digits after the T indicate stress relief:
TX51 or TXX51 – Stress relieved by stretching.
TX52 or TXX52 – Stress relieved by compressing.

What to know more? Download a complete guide to aluminum extrusion tempers.

Rather than attempt to become an alloy expert, engage your aluminum extrusion manufacturer early in the design process. Discuss the component or product’s end-use and your specific requirements, such as strength, environmental conditions, finish, and fabrication needs, and let the extruder’s engineer make suggestions. These are experts waiting to help you make the best product possible—a valuable resource that every designer should take advantage of.

Disclaimer: This content is provided solely for the purposes of providing information about the aluminum extrusion process and use of aluminum alloys. Vitex does not make any guarantee or promise about how an alloy may perform under the extrusion techniques noted.