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Temper Designations for Aluminum


Aluminum is known for its versatility; while properties such as superb resistance to corrosion and excellent thermal conductivity are very useful in many applications, it is the flexibility and adaptability of aluminum’s mechanical properties that make it such a widely used metal. The mechanical properties of aluminum can be altered through various means (e.g. adding alloying elements or work hardening).

One of the most popular methods of altering the mechanical properties of some grades of aluminum is through tempering. Since tempering can have such a pronounced effect on an aluminum alloy, it is extremely important to be able to comprehend what the tempering designations of aluminum are and what they mean so that misunderstandings do not result in fracturing and failure.

What is Temper in Aluminum?

Temper in relation to aluminum refers to the various conditions achieved through mechanical and thermal treatments, which alter the physical properties of the metal to meet specific performance criteria. These treatments can affect strength, ductility, hardness, and resistance to stress and corrosion. The temper designations for aluminum alloys help engineers and manufacturers select the appropriate material for their needs.

What is an Aluminum Tempering Designation?

An aluminum tempering designation is a series of letters and numbers that are used to denote what type of tempering treatment an aluminum alloy has undergone. The temper designation is preceded by a dash and placed after the aluminum alloy designation (e.g. 6061-T6). Understanding what an aluminum temper designation means is critical to picking the correct material. It is important because an aluminum alloy can be exactly the same in terms of chemical makeup as another aluminum alloy, but if the two have different tempering designations, then the mechanical properties of both alloys could be vastly different.

What are the Aluminum Tempering Designations?

There are four main types of aluminum tempering designations. The types are denoted by a letter that precedes a number. The four letter designations are:

  • T: Thermally treated
  • H: Strain hardened
  • O: Annealed
  • F: As fabricated

Following the letters of an aluminum temper designation are numbers. The temper number specifies how the tempering method was performed. For instance, a T5 and a T6 are both thermally treated; however, a T5 indicates that the aluminum alloy was cooled from a high-temperature shaping process and artificially aged, whereas a T6 was solution heat treated and then artificially aged. The difference in a number in an aluminum temper designation can inform the purchaser of an aluminum alloy about a nuance that could have a significant impact on the mechanical properties of the alloy.

While there are many variations of temper numbers that can be used, the “T” number variations are perhaps the most commonly used and important to understand. Here are descriptions of some of the “T” designation number variants:

  • T1: Naturally aged after cooling from an elevated temperature from a forming process
  • T2: Cooled from an elevated temperature forming process, cold worked, then naturally aged
  • T3: Solution heat treated, cold worked, then naturally aged
  • T4: Naturally aged after a solution heat treatment
  • T5: Artificially aged after cooling from an elevated temperature from a forming process
  • T6: Artificially aged after cooling from a solution heat treatment
  • T7: Solution heat treated, then overaged
  • T8: Solution heat treated, cold worked, then artificially aged
  • T9: Solution heat treated, artificially aged, then cold worked
  • T10: Cooled from an elevated temperature forming process, cold worked, then artificially aged

For the meaning of the numbers that follow letter temper designations such as “O”, “H”, and “F”, it is best to consult an aluminum temper chart or get a technical data sheet on the aluminum alloy to determine exactly what the temper designation means.

How to Read an Aluminum Temper Chart?

Reading an aluminum temper chart starts with identifying the temper code. This combination includes a temper letter followed by a temper number that represents the alloy’s specific treatment process and resultant properties. Once you locate the temper code, cross-reference it with its description provided in the chart to understand the mechanical or thermal treatment the aluminum has undergone.

Examine the mechanical properties listed alongside each temper designation, such as tensile strength, yield strength, and elongation. This data is essential for assessing the material’s performance characteristics. Use this information to determine the suitability of a specific aluminum temper for your application, ensuring it meets your performance criteria. Some charts may include annotations or footnotes offering extra context or exceptions for certain tempers.

Some Common Examples of Aluminum Alloy Tempers and Their Applications

Many different temper designations exist for aluminum alloys, but some are more prevalent than others, especially for certain uses. Here are some of the most popular aluminum alloy temper designations and their applications:

  • 2024-T4: Aircraft structures, fasteners, hardware, wheels, screw machine products
  • 3003-H14: Food and chemical handling equipment, tanks, trim, litho sheet, pressure vessels, and pipes
  • 5052-H32: Aircraft fuel/oil lines, fuel tanks, transportation, appliances, lighting, wire, and rivets
  • 6061-T6: Aircraft fittings, camera lens mounts, couplings, marines fittings and hardware, electrical fittings and connectors, decorative or misc. hardware, hinge pins, magneto parts, brake pistons, hydraulic pistons, appliance fittings, valves and valve parts
  • 6063-T5: Pipes, railings, furniture, architectural extrusions, irrigation pipes, and transportation
  • 7075-T6: Aircraft fittings, gears and shafts, fuse parts, meter shafts and gears, missile parts, regulating valve parts, worm gears, keys, aircraft, aerospace and defence applications; bike frames, all-terrain vehicle (ATV) sprockets

Why Do I Need to Understand Temper Designations for Aluminum Alloys?

By knowing the properties associated with different temper numbers, such as tensile strength, ductility, and resistance to stress and corrosion, you can choose the most suitable aluminum temper for your application. It will help ensure optimal performance and longevity while reducing the likelihood of product failure, which can be costly and time-consuming.

A thorough understanding of temper designations for aluminum alloys can help maintain consistency and quality across production batches. It allows for better communication and collaboration with suppliers and clients, as everyone involved speaks the same technical language regarding material specifications.


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