Understanding Aluminum Hardening Processes T0, T4, T5, and T6

Differences and Applications

In the modern manufacturing industry, aluminum has become one of the most essential materials. Lightweight, corrosion-resistant, and highly formable, aluminium is widely used across various sectors from construction and transportation to high-tech industries.

However, not all aluminium has the same properties. Two extrusion profiles that appear identical can have significantly different strength and hardness levels, depending on the heat treatment applied. This condition is known as the aluminium temper, which defines the material’s hardness and mechanical properties after specific thermal processes.

This article explores the aluminium hardening processes T0, T4, T5, and T6, covering their manufacturing stages, key characteristics, and industrial applications.

What Is Aluminum Heat Treatment?

Pure aluminum has a relatively soft crystal structure. To enhance its strength and hardness, aluminum is alloyed with elements such as magnesium (Mg) and silicon (Si). These combinations form aluminum alloys that can be strengthened through heat treatment.

The principle is straightforward: the metal is heated to a high temperature, rapidly cooled, and then allowed to “age.” This process modifies the metal’s microstructure, forming fine precipitates (such as Mg₂Si particles) that strengthen the crystal lattice from within.

This is what distinguishes soft aluminum from hardened aluminum—not the alloy composition itself, but the thermal treatment applied.

General Stages of Aluminum Hardening

Solution Heat Treatment

The aluminum is heated to approximately 500–540°C, allowing the alloying elements to dissolve completely into the metal structure.

Quenching (Rapid Cooling)

After heating, the metal is rapidly cooled using air, water, or pressurized air. This step “locks” the alloying elements in place before they can precipitate.

Aging

The aluminum is then left to mature so that fine precipitates can form. Aging can occur naturally at room temperature (natural aging) or artificially in an oven at 150–200°C for several hours (artificial aging).

These combinations of processes result in different aluminium tempers such as T0, T4, T5, and T6.

Aluminium Temper T0 Soft and Highly Formable

T0, commonly referred to as the annealed temper, is the softest aluminium condition. At this stage, the material undergoes no hardening. Aluminium that has been cold-worked (rolled or drawn) is reheated to restore a uniform structure and eliminate internal stress.

Key characteristics:

Low tensile strength, approximately 60–90 MPa
Extremely ductile and easy to form, weld, or bend without cracking
Unsuitable for load-bearing applications, but ideal for forming and deep drawing

Typical applications:

Decorative components, nameplates, and lightweight architectural elements
Products that will undergo further processing before being hardened to T4 or T6

T0 can be considered a “blank canvas”—easy to shape first, then strengthened later.

Aluminium Temper T4 – Solution Heat Treated and Naturally Aged

T4 aluminum undergoes solution heat treatment followed by natural aging. This process increases strength compared to T0 while maintaining excellent formability.

Key characteristics:

Medium tensile strength (approximately 130–190 MPa for 6063-T4)
Good ductility, suitable for bending, riveting, and post-forming
Naturally cooled and aged at room temperature

Typical applications:

Automotive body panels, curved architectural structures, and components requiring further shaping
Widely used in the automotive industry for door and body panels

T4 represents a “semi-hardened” state strong enough for handling yet flexible enough for further fabrication.

Aluminum Temper T5 Artificially Aged After Extrusion

T5 aluminum is cooled directly after extrusion and then subjected to artificial aging, without a separate solution heat treatment. This approach shortens production time while achieving sufficient strength.

Key characteristics:

Moderate to high strength with limited flexibility
Ideal for extrusion products with no post-forming
Excellent dimensional stability

Typical applications:

Aluminum window frames, door systems, façade panels, and light structural components
Commonly produced using 6063-T5 alloy for its balance of strength and aesthetic finish

T5 is favored by extrusion manufacturers due to its cost efficiency, speed, and reliable mechanical properties.

Aluminum Temper T6 Maximum Strength and Hardness

T6 is achieved through solution heat treatment followed by artificial aging, making it the strongest and hardest condition among T0–T6 tempers. After extrusion, the aluminum is heated until the alloying elements dissolve completely, quenched in water, and then aged in an oven at 175–200°C for 6–8 hours.

Key characteristics:

Highest strength and stiffness
Lowest ductility; not suitable for bending after hardening
Excellent structural stability and deformation resistance

Typical applications:

Automotive and aerospace frames, machine components, high-performance heat sinks, and heavy load-bearing structures
Popular alloys include 6061-T6 (automotive and industrial use) and 6082-T6 (structural construction)

T6 represents the final hardened form strong, rigid, and durable but shaping must be completed prior to the heat treatment process.

How to Choose the Right Aluminium Temper

Selecting the appropriate temper is not simply about choosing the hardest option. Each application has different priorities:

Maximum formability: T0 or T4
Production efficiency with moderate strength: T5
High strength and rigidity: T6

Key considerations include:

Aluminium alloy type (e.g., 6061, 6063, 6082)
Profile geometry and design
Production factors such as cost, time, and finishing requirements

Conclusion

The differences between T0, T4, T5, and T6 are more than technical codes—they reflect the metallurgical processes that define aluminium’s strength, flexibility, and durability.

T0 → highly formable
T4 → flexible yet strong
T5 → efficient and dimensionally stable
T6 → high strength and load resistance

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Consult Your Aluminum Solutions with Exalum Metal

If you require high-quality aluminum extrusion products with precise temper control and heat treatment, Exalum Metal is your trusted partner. As an experienced manufacturer and industrial supplier, Exalum Metal manages every production stage from profile design and extrusion to advanced heat treatment and premium finishing.

Visit Exalum Metal Our Process to learn more about our extrusion technology and explore our wide range of aluminum products used across multiple industries.

With proven expertise in aluminum hardening processes from T0 to T6, Exalum Metal is ready to deliver strong, precise, and long-lasting aluminum solutions tailored to your needs.

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