Different Types Of Aluminum Tempering

March 1, 2021

What are the different types of aluminum tempering? 

  1. Fabricated (F)
  2. Annealed (O)
  3. Strain-hardened (H) 
  4. Solution heat-treated (W)
  5. Thermally treated (T) 

It is the versatility of aluminum that makes it such a widely used material. As an alloy, aluminum can be treated through a variety of means and one of the most popular methods of treatment is tempering. The purpose of different types of aluminum tempering is to create alterations within the alloy’s grain structure and hardness. 

There are certain types of aluminum profile in the Philippines that can go through tempering. Among its many advantages for applications include good corrosion resistance, durability, and ductility, which makes it easier to be formed by various fabrication processes without fracture. 

What Are Temper Designations? 

Aluminum products with specific properties are categorized by alloy and temper designations. Alloy designations are four-digit numbers, which determine the alloy chemistry. Alternatively, temper designations are denoted by alphanumerics that are added after the four-digit alloy designation. An example would be 6061-T6 where -T6 is the temper designation.

It can be challenging to make sense of temper designations. Nonetheless, it is extremely vital to recognize what these mean as tempering significantly influences the properties of aluminum products. It allows manufacturers to tell whether the aluminum has been treated beforehand and therefore, avoid fracturing. 

In this article, you’ll find the different temper designations that define aluminum also known as the types of aluminum tempering. Continue reading to learn more.

Fabricated (F) 

Fabricated aluminum tempering applies to alloy products formed by rolling, forging, casting, or extrusion wherein no special control over the thermal nor strain hardening treatments has been performed. Fabricated aluminum tempering is one of the most common forms of tempering that’s designed with no improvement limits in the physical and mechanical properties of the alloy. 

Most fabricated temper products are “semi-finished” and will be used in shaping or finishing other finished forms of aluminum. For instance, aluminum can be utilized for products that have been rolled, forged, cast, extruded, or any combination of these processes

Annealed (O) 

Coils of aluminum on the table before annealing process

The purpose of annealed aluminum tempering is to reset the crystalline grain structure to acquire the softest temper, which restores deformations. It removes any prior thermal treatment. The resulting desirable property achieved is an aluminum product that has maximized workability, increased durability, and ductility. One can shape the alloy without requiring excessive force and even prevents fractures. 

To anneal an aluminum, the alloy must be heated between 570°F to 770°F for a certain amount of time, which can depend on the size or composition of the alloy. This can range anywhere from 30 minutes to 3 hours. 

Annealed aluminum tempering can also stability the dimensions of the alloy during processes such as casting or cold forging. This also resolves issues that develop from strains like warping. 

Annealing can be successfully performed on aluminum that is non-heat treatable. It is typically used for extruded, forged, or casted aluminum.  

Strain-Hardened (H) 

Aluminum is subject to strain hardening to have increased its strength usually at room temperature. This type of tempering may or may not apply to alloys that have thermal treatments. It is a process to make alloys durable through cold working.  

When an alloy goes through cold works, dislocations are formed and defect the grain structure. These dislocations and defects reduce the ability of grain structures and therefore, result in more resistance to deformation. The resulting aluminum has improved strength and hardness, but with less ductility. 

Think of it as a wire bent back and forth. Notice how it becomes more difficult to bend the wire at the same place. With strain-hardened aluminum tempering, the wire material is strengthened. 

The “H” in this tempering type is always followed by digits, which indicates the operation and degree of strain hardening. The main types are as follows: 

  • H1 – Strain hardened only
  • H2 – Strain hardened and partially annealed
  • H3 – Strain hardened and stabilized
  • H4 – Strain hardened and painted 

Solution Heat-Treated (W)

L-profiled aluminum inside a factory

This type of aluminum tempering applies only to alloys that are aged naturally — one where the strength changes at room temperature over a period of time after thermal treatment. This is seldom encountered because it is an unstable and rarely a finished temper. The digits following the “W” can be added to characterize the elapsed time since the cooling took place. An example would be 6061-W½. 

Thermally Treated (T) 

This applies to any aluminum temper that is heat-treated, with or without subsequent strain hardening. It is followed by quenching (cooling) and either natural (e.g. air) or artificial (e.g. in a furnace) aging. 

The “T” is always succeeded by digits that define the treatments. These are discussed below: 

  • T1 – Cooled from a high-temperature shaping process and naturally aged to a stable condition.
  • T2 – Cooled from a high-temperature shaping process, cold worked, and naturally aged to a stable condition.
  • T3 – Alloy is heat-treated, cold worked, and naturally aged to a stable condition.
  • T4 – Alloy is heat-treated, and naturally aged to a substantially stable condition.
  • T5 – Cooled from a high-temperature shaping process and artificially aged.
  • T6 – Alloy is heat-treated then artificially aged.
  • T7 – Alloy is heat-treated then overaged or stabilized.
  • T8 – Alloy is heat-treated, cold worked, then artificially aged.
  • T9 – Alloy is heat-treated, artificially aged, then cold worked.
  • T10 – Cooled from a high-temperature shaping process, cold worked, then artificially aged.

Key Takeaway

As you’ve learned, there are different types of aluminum tempering. With these, manufacturers have been able to optimize the properties of aluminum alloy. These can range from corrosion resistance, ductility, and durability. The resulting products are advantageous for numerous applications.