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BlogMachining and Fabrication Design Tips

How to Read Aluminum Alloys and Tempers

Properties of aluminum materials can vary significantly based on alloy composition and how that alloy is tempered after its creation. Read this article to learn more about aluminum alloys within the standard naming system.

By Greg Paulsen
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Aluminum is a metal that combines robust mechanical properties with low weight. It is significantly lighter than other metal counterparts, such as steels. Many applications are weight-sensitive, so the use of aluminum in vehicular, aircraft, spaceflight, and equipment designs is very common. Aluminum materials are most often formed from casts or extrusions and are go-to materials for CNC machining and sheet metal parts.

Not all aluminum stock is the same. Properties of aluminum materials can vary significantly based on alloy composition and how that alloy is tempered after its creation. Aluminum alloy is defined using standard naming, this article helps better understand the aluminum alloy designation system.

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  • Annotation of Aluminum Alloy Nomenclature

The specification of aluminum alloy can be broken down by its series, temper, and conditions.

An additional suffix after tempers can signify the wrought product type for even more specific material specifications. The example table below shows the classifications for aluminum 7075-T7351.

Classifications for Aluminum 7075-T7351
Letter Indicator in 7075-T7351
7XXX-seriesZinc-alloyed aluminum in a plate, rod, or bar form
T7Solution heat-treated, stretched a controlled amount for stress-relieving
351Artificially overaged to provide superior corrosion resistance

A breakdown of what each character in aluminum 7075-T7351 means for that specific alloy.

Understanding Aluminum Series

Aluminum is typically alloyed with other elements to produce different strengths. These alloys are defined by strength in their series, with labels ranging from 1xxx- to 7xxx-series depending on the alloying agents used. The chart below shows different alloy series and what makes them unique.

Types of Aluminum Alloys
Alloy SeriesAlloying Agent(s)DescriptionExamples
1xxx99%+ Pure AluminumIs soft, ductile, and easily welds. Is not heat-treatable.Aluminum 1100
2xxxCopperHas high strength and durability and requires corrosion protection.Aluminum 2024
3xxxManganeseIs highly ductile, great for bending, and best suited for forming.Aluminum 3003
4xxxSiliconHas a lower melting point and is used as a welding wire.Aluminum 4032
5xxxMagnesiumHas high strength and malleability, is great for bending, and is corrosion-resistant.Aluminum 5052
6xxxMagnesium + SiliconHas high strength and formability. Is weldable, heat-treatable, and corrosion resistant. Has wide range of use across industries.Aluminum 6061, Aluminum 6063
7xxxZincHas very high tensile strength and stiffness as well as high usage in aerospace designs. Is not suitable for bending.Aluminum 7050, Aluminum 7075

Wrought aluminum alloy lookup table. 2xxx, 5xxx, 6xxx, and 7xxx-series are the most typical alloys used in aerospace and defense.

The secondary numbers before the temper are specific alloy compositions per aluminum series. 6XXX-series aluminum, like 6061, is very popular because it does not work-harden quickly, allowing greater ease of raw material manufacturing through the extrusion of profiles. This reduces the costs of raw stock material fabrication. The material is also easily CNC milled for custom manufacturing. However, 6061 may be too brittle for rolling or forming. This is why 5XXX-series aluminum, like 5052, is most common in sheet metal fabrication or stamping applications.

An alternative to wrought billets is cast aluminum. This material provides a near-net-shape of the product. MIC-6 is a cast 5083 aluminum that is used for tooling plates and test fixtures.

Understanding Aluminum Tempers

To classify aluminum types beyond the net shape and strength of the alloy, temper is used in the naming series. Tempers add additional mechanical properties through rapid cooling (quenching), cold working, or precipitation heat treatment combinations.

Aluminum and alloys from 1XXX-, 3XXX-, 4XXX-, 5XXX-series can not be heat treated but can be strain hardened. This is signified with a suffix of -H##. Strain hardening strengthens a material through cold working. For example, Aluminum 5052-H32. 2XXX-, 6XXX-, and 7XXX-series aluminum can be precipitation hardened, or heat-treated, signified by a -T#, such as 6061-T6. The following reference chart depicts different aluminum tempers.

Reference Table for Different Aluminum Tempers
Extrusion TemperDescription
FExtruded, air-cooled with no special controls
OFully annealed to the lowest strength temper
H2Strain-hardened and partially annealed
H3Strain-hardened and stabilized
H4Strain-hardened and lacquered or painted
WSolution heat-treated
T1Cooled from an elevated temperature and naturally aged
T2Cooled from an elevated temperature, cold-worked, and naturally aged
T3Solution heat-treated, cold-worked, and naturally aged
T4Solution heat-treated and naturally aged
T5Cooled from an elevated temperature and artificially aged
T6Solution heat-treated and artificially aged
T7Solution heat-treated and stabilized
T8Solution heat-treated, cold-worked, and artificially aged
T9Solution heat-treated, artificially aged, and cold-worked
T10Cooled from elevated temperature, cold-worked, and artificially aged

Extrusion temper lookup chart. Tempers may have multiple digits after a letter to indicate sub-classifications in each temper, material age condition, and final state.

Looking Beyond Aluminum Alloys and Tempers

Beyond tempers, there may be additional suffix classifications that are specific to that series/temper combination. The Metallic Materials Properties Development and Standardization Handbook, MMPDS-14, is a powerful reference for more complete definitions and standards of metals used in manufacturing.

This excerpt was inspired by Xometry’s ebook: Custom Manufacturing for Aerospace and Defense. You can get an instant quote on custom CNC or sheet metal projects here.

Greg Paulsen
They call me the Director of Application Engineering at Xometry. This means I not only get to produce great design-for-manufacturing content, but also consult on a variety of custom manufacturing projects using CNC machining, additive manufacturing, sheet metal, urethane casting, and injection molding. If you have a question, I'm your guy.

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