For manufacturers, engineers, and procurement professionals working with aluminum materials, it is crucial to understand how to read aluminum alloys and their corresponding tempers. Designation system of aluminum alloy- This system has standard techniques of identifying material properties, composition, and conditions to which it is treated that have a direct relation with the manufacturing application.

Guidance to the System of Aluminum Alloy Designations

The Aluminum Association came up with the modern aluminum alloy system to standardize the identification of more than 400 registered aluminum alloys. This extensive system employs a four-digit numbering system of wrought alloys and a three-decimal point system of cast alloys, allowing materials to be specified to the required level throughout manufacturing facilities worldwide.

Wrought Aluminum Alloys Classification

The wrought aluminum alloys essentially use a four-digit alloy system in which the first number denotes the major alloying ingredient. This classification method allows engineers to quickly identify material characteristics: 

• 1000 Series: Minimum 99 percent aluminum content–excellent corrosion resistance, excellent thermal conductivity. 
• 2000 Series: Copper as major alloy component – high strength, aerospace
• 3000 Series: Manganese as a main alloying element – Medium strength, Good working 
• 4000 Series: Silicon as a main alloying element – Low melting, welding use 
• 5000 Series: Magnesium as a main alloying element- Best corrosion resistant, marine applications 
• 6000 Series: Magnesium and silicon – Best strength/weight use, structural applications 
• 7000 Series: Zinc as a main alloying element – Strongest aluminum alloy, 
• structural use 8000 Series

Designation Cast Aluminum

Cast aluminum alloys use a unique three-digit plus decimal nomenclature (XX.XX), with the decimal number after the third character, denoting a casting (.0), ingot (.1 or 2) operation.

How to Read Aluminum Alloys and Tempers: Decoding the Numbers

Learning how to read aluminum alloys and tempers requires understanding both the alloy designation and temper classification. The specification can be broken down by series, temper, and conditions, with additional suffixes signifying specific wrought product types.

The Four-Digit Alloy Code

As an example, with 6061.

• First digit (6): Displays the 6000 series, which has magnesium and silicon
• Second digit (0): Standard alloy, no modifications
• Third and fourth digits (61): Specific alloy identification within the series

6061 T6 Aluminum: Industry Standard Example

6061-T6 represents one of the most popular aluminum grades, offering tensile strength of 290 MPa (42 ksi) and yield strength of 240 MPa (35 ksi). The T6 designation indicates solution heat treatment followed by artificial aging, providing optimal precipitation hardening.

Aluminum Temper Codes: Understanding Material Conditions

The temper designation system addresses material conditions through a series of letters and numbers connected by a hyphen to the alloy designation. These codes communicate the thermal and mechanical treatments applied to achieve specific properties.

Primary Temper Designations

F – As Fabricated: Wrought or cast aluminum shaped without regard to specific temperatures or strain hardening

O – Annealed: Heat-treating process that softens strain-hardened aluminum for further working or applications where over-hardening is a concern

H – Strain Hardened: Non-heat-treatable alloys that have been worked to strain harden the aluminum, with greater working providing increased resistance to further working

T – Thermally Treated: Applies to heat-treatable alloys that have been aged following solution heat treatment

W – Solution Heat Treated: Unstable condition requiring natural aging at room temperature

H Temper Subdivisions for Aluminum Temper Codes

The H temper uses a three-digit system:

H1X – Strain Hardened Only: Products strain-hardened to obtain desired mechanical properties without supplementary thermal treatment

H2X – Strain Hardened and Partially Annealed: Materials strain-hardened beyond the desired amount, then reduced through partial annealing

H3X – Strain Hardened and Stabilized: Products strain-hardened and stabilized by low-temperature heating to lower strength and increase ductility

The second digit indicates the strain hardening degree:

• 2: Quarter hard
• 4: Half hard
• 6: Three-quarters hard
• 8: Full hard

T Temper Classifications

T temper designations specify thermal treatment sequences, with T1 through T10 indicating different combinations of solution treatment, aging, and cold working:

T1: Naturally aged after cooling from the elevated temperature forming process. T4: Solution heat-treated and naturally aged to a stable condition
T5: Cooled from elevated temperature shaping process and artificially aged T6: Solution heat treated and artificially aged T7: Solution heat treated and stabilized (overaged)

Aluminum Series Classification: Properties and Applications

Knowledge of aluminum classification in series helps one to select the right material depending on the particular production needs. The alloys of the 1xxx and 3xxx, and 5xxx series are not all heat treatable, whereas those of the 2xxx, 6xxx, and 7xxx series are all heat treatable.

Heating of Alloys: Heat-Treatable and Non-Heat-Treatable Alloys

6xxx, 2xxx, and 7xxx series are referred to as Heat-Treatable series:

• Achieve strength through precipitation hardening
• Can be solution-treated and aged
• Higher strength potential
• More complex processing requirements

Non-heat treatable Series (1xxx, 3xxx, 5xxx)

• Achieve strength through strain hardening
• Cannot be strengthened by heat treatment
• Simpler processing
• Excellent corrosion resistance

Popular Wrought Aluminum Alloys Applications

2024-T4: Aeronautical structural parts, high strain usage 

5052-H32: Marine uses, policy of chemical equipment

6061-T6: Framing, automotive, general manufacturing 

7075-T6: Aircraft structures, high-performance application

Reading Complete Aluminum Specifications

When learning how to read aluminum alloys and tempers, consider this complete example: 7075-T7351

• 7075: 7000 series zinc alloy with high strength
• T7: Solution heat-treated and stabilized
• 3: Cold worked after solution treatment
• 5: Stress relieved by stretching
• 1: To specific dimensional tolerances

Process Section: Considerations to Make When Manufacturing Aluminum

During the manufacturing process, the properties taken into account in material selection refer to mechanical, fabrication, and environmental considerations, and those of cost effectiveness to achieve optimal manufacturing results.

Key Selection Factors

• Strength Requirements: Match temper designation to load requirements 
• Corrosion Resistance: Consider environmental exposure conditions
  Weldability: Some tempers lose strength during welding.
• Machinability: T6 tempers generally machine better than annealed conditions. 
• Formability: Softer tempers allow more complex forming operations

6061 T6 Aluminum Advantages

6061-T6 has a good strength-to-weight ratio, excellent corrosion resistance, and much better machinability than annealed conditions. The combination makes it applicable to parts that need moderate to high strength, but good fabrication quality of the structure.

Quality Control and Material Verification

Proper material identification requires verification of both alloy composition and temper condition. Material certificates should specify the complete designation, including any additional temper suffixes that affect mechanical properties.

Testing and Documentation

Manufacturing quality systems should verify:

• Chemical composition compliance with the specification
• Mechanical property confirmation through testing
• Temper verification through hardness or tensile testing
• Traceability documentation for critical applications

Industry Standards and References

The Aluminum Association international alloy designation system is based on ANSI H35.1, with international recognition being derived through harmonization agreements with eighteen countries and the European Aluminum Association.

Understanding how to read aluminum alloys and tempers requires familiarity with these industry standards to ensure proper material specification and procurement. Producing activities are in favor of designation systems with standardization, which makes it easier to communicate within the worldwide supply chain.

FAQs

1. What does the T6 rating mean in aluminum alloy?

T6 implies that this alloy of aluminum has been subject to the solution heat treatment followed by artificial aging. It is done by heating the material to a temperature over 900°F and then cooling in water, and then aging at a lower temperature with the aim of maximum precipitation hardening and strength.

2. What are the telltale signs that an aluminum alloy is heat treatable?

Aluminum alloys that can be heat-treated include 2xxxx, 6xxxx, and 7xxxx, whereas the 1xxx, 3xxx, and 5xxx series of aluminum alloys cannot be heat-treated. Alloys that are heat treatable may be hardened by way of solution treatment and hardening.

3. What is the distinction between 6061 and 6063 aluminum?

Both are Mag and Silicon 6000 series, with 6061 being stronger and used with structural parts, and 6063 has a superior looking and corrosion resistance, used in architectural situations such as windows and door frames.

4. Are aluminum alloy tempers converted at some point after fabrication?

Yes, most of the alloys of aluminum are re-heat treatable to alter their temper condition. Instead, welding shall normally decrease T6 temper properties to about T4, and post-weld heat treatment again is necessary to reclaim full strength.

5. What do past the T6 represent (such as T651)?

Additional digits specify stress relief treatments. T651 indicates the material was stress relieved by stretching after solution treatment and aging, while T652 indicates stress relief by compression.