How to Choose the Right Aluminium Temper: H vs. T Series Explained

In the world of aluminium, the alloy grade (such as 6061 or 3003) determines its chemical composition, while the temper designation that follows (like T6 or H32) directly defines its mechanical properties—such as strength, hardness, and ductility. For engineers, designers, and purchasers, understanding and correctly selecting the aluminium temper is crucial to the success of a project. This article provides a clear aluminium tempers guide, focusing on the two most common temper series: H (Strain-Hardened) and T (Heat-Treated), to help you make an informed decision.

Key Difference: The Nature of the Process

*   H Series (Strain-Hardened Tempers): Primarily strengthened through cold working processes like rolling, stretching, or drawing. This mechanical deformation makes the aluminium stronger and harder but typically reduces its ductility. The H series is mainly used for non-heat-treatable alloys, such as those in the 1xxx, 3xxx, and 5xxx series.

*   T Series (Heat-Treated Tempers): Strengthened through a precise heat treatment process involving solution heat treatment, quenching, and aging. This process changes the alloy’s internal structure to significantly enhance its strength. The T series is designed for heat-treatable alloys, such as those in the 2xxx, 6xxx, and 7xxx series.

In simple terms, the H series achieves strength through “physical exercise” (work-hardening), while the T series develops ultra-high strength through “internal transformation” (heat treatment).

The H Series Explained & Common Designations

An H designation is followed by two or three digits (e.g., H14, H32).

*  The first digit indicates the specific sequence of basic treatments:

*  H1X: Strain-hardened only. For example, H18 is the full-hard temper.

*  H2X: Strain-hardened and then partially annealed. For example, H28 is hard but slightly softer than H18.

*  H3X: Strain-hardened and then stabilized by low-temperature heat treatment. This is particularly suitable for magnesium-containing 5xxx alloys, improving resistance to stress corrosion cracking. H32 is a very common designation.

*   The second digit indicates the degree of hardness, with a higher number representing greater strength/hardness and lower ductility.

When to Choose It:

*   Typical Applications: Sheet metal enclosures (3003-H14), marine plates (5052-H32), can ends, lighting fixtures, architectural panels.

*   Choose the H series when you need good formability (especially H2X/H3X tempers), excellent corrosion resistance, and moderate strength.

The T Series Explained & Common Designations

A T designation is followed by one or more digits (e.g., T6, T651).

*   T4: Solution heat-treated and naturally aged. Offers moderate strength and good formability.

*   T5: Artificially aged after cooling from a high-temperature shaping process (like extrusion). Stronger than T4.

*   T6: Solution heat-treated and artificially aged. This is the most common heat-treated temper, providing the highest strength for the alloy.

*   T651: This designation indicates the material has been stress-relieved by stretching in addition to the T6 treatment. This greatly reduces internal stress, meaning the material is much less likely to warp during machining, offering superior dimensional stability.

When to Choose It:

*   Typical Applications: Aerospace components (7075-T651), automotive frames & parts (6061-T6), bicycle frames, high-strength mechanical parts, precision-machined components.

*   Choose the T series when your design demands high strength, hardness, and excellent machinability. For critical machining applications, choose T651 for better stability.

H Series vs. T Series: A Quick Selection Guide