The Aluminum Numbering System

Aluminum is normally alloyed with several different elements in order to improve the mechanical or chemical properties. As a result, there are a large number of combinations of alloying elements that can be used to achieve the desired properties, resulting in a wide variety of aluminum grades. To help make sense of all these combinations, an aluminum numbering system is used.

What is the Aluminum Numbering System?

The Aluminum Association created the nomenclature, and it is the organization that maintains the designation system. There are many different rules for labeling the various types of aluminum alloys. First, it is important to know whether the aluminum alloy is wrought or cast.

Wrought Aluminum

Wrought aluminum alloys use a four-digit system. The first digit is used to designate the primary alloying element. As an example, a 1XXX alloy indicates a mostly pure aluminum alloy, whereas a 6XXX alloy indicates that significant amounts of magnesium and silicon have been added to the aluminum. Below is a table for the different alloying elements of wrought aluminum:

The second digit in the wrought aluminum numbering system indicates that there has been a special modification to one of the alloying elements. These controls are registered with IADS and require the specific IADS documentation. The third and fourth digits in the wrought alloy aluminum designation system are used to label the specific alloy. These numbers are arbitrary except for the 1XXX series of aluminum. In the 1XXX series, the last two digits specify the minimum aluminum content between 99% and 100%. For example, 1060 aluminum would have a minimum pure aluminum content of 99.60%.

Cast Aluminum

Cast aluminum alloys use a four-digit system that includes a decimal point (XXX.X). Similar to wrought aluminum, the first digit in the cast aluminum alloy designation system indicates the major alloying element or elements. The table below features the different alloying elements assigned to each digit:

The second and third digits of the cast aluminum numbering system are also arbitrary, indicating the aluminum alloy, with the exception of the 1XX.X series. Similar to the wrought aluminum alloy designation system, the second and third digits for these grades are used to indicate aluminum purity above 99%. The final digit after the decimal point is used to mark whether the aluminum alloy is a casting or an ingot. A “0” indicates a casting, while “1” indicates an ingot.

Temper designations can follow the digits for both wrought and cast aluminum alloys. They show how the aluminum has been processed and can affect properties such as strength and hardness. The “F” designation means fabricated with no special treatment, “H” means strain hardened, “O” means annealed, and “T” covers thermally treated conditions. The “W” designation means solution heat-treated and refers to an unstable condition that can change as the alloy naturally ages. These designations are important when later processing could alter the material’s condition. The 2XXX, 6XXX, 7XXX, and some 4XXX wrought alloys are heat treatable, along with certain cast alloy families such as 2XX.X, 3XX.X, 4XX.X, and 7XX.X.

What Each Aluminum Series Is Used For

The aluminum group number can quickly point you toward the right family of alloys. Some series are better for forming, some for strength, and others for corrosion resistance, machining, or general fabrication.

1xxx and 3xxx for Forming and Corrosion Resistance

The 1xxx and 3xxx series work well when the part needs to bend, form, or hold up against corrosion. Alloy 1100 is often used for cookware, chemical equipment, and panels. Alloy 3003 adds more strength while keeping good workability, making it common in tanks, roofing, ductwork, and other sheet-metal parts.

2xxx and 7xxx for High-Strength Parts

The 2xxx and 7xxx series are often used when strength matters more. Alloy 2024 is known for high strength and fatigue resistance, while 7075 is one of the strongest aluminum alloys available. Alloy 2011 is different from most 2xxx grades because it is mainly valued for machinability and is often used for turned parts.

5xxx for Marine and Corrosion-Resistant Parts

The 5xxx series is a strong option for parts exposed to moisture or saltwater. Alloy 5052 combines good corrosion resistance with good formability, which makes it common in marine parts, fuel tanks, enclosures, appliances, and formed sheet-metal components.

6xxx for General Fabrication and Structural Work

The 6xxx series is widely used because it offers a good mix of strength, machinability, weldability, and corrosion resistance. Alloy 6061 is common in frames, structural parts, machined components, and welded assemblies. Alloy 6063 is often used for architectural extrusions, trim, and parts that need a clean finish or anodized surface.

How to Narrow Down the Right Aluminum Grade

The aluminum alloy numbering system can point you in the right direction, but the best grade still depends on what the finished piece needs to do.

Start With the Application

Think about how the material will be used. Does it need to carry weight, resist corrosion, bend into shape, be welded, or be cut and drilled easily? A formed panel, welded bracket, and machined fitting may each need different aluminum alloys.

Check the Temper

The temper tells you how the aluminum was treated after it was made, such as by heating or hardening it. This can change its strength, hardness, and how easily it bends. Two pieces of the same grade can perform differently, so check both the grade and temper before ordering.

Factor In Machining and Welding

Some grades are easier to cut, drill, or shape with tools, while others are better suited to welding. Alloy 2011 is often used for machined parts, while 6061 is a common choice for welded and fabricated components. These requirements can help narrow down the right aluminum group number.

Match the Grade to the Shape You Need

Not every grade is available in every form. Aluminum sheet comes in grades such as 1100, 2024, 3003, 5052, 6061, and 7075. Aluminum round bars include grades such as 2011, 2024, 6061, and 7075. Check the grade and shape together so you know the material is available in the form your job requires.

Metal Supermarkets stocks a wide range of aluminum and aluminum alloys in different grades and shapes, cut to your specifications.

Frequently Asked Questions About Aluminum Alloy Numbers

What do aluminum alloy numbers mean?

Aluminum alloy numbers identify the alloy family and give you a quick clue about the metal’s composition. In wrought aluminum, the first digit points to the main alloying element, such as magnesium in the 5xxx series or magnesium and silicon in the 6xxx series. The full grade and temper then tell you more about how the material is likely to perform.

How do I know which aluminum alloy to use?

Start with what the finished part needs to do. If corrosion resistance and forming matter, a grade such as 5052 may be a good fit. If you need a balance of strength, machinability, and weldability, 6061 is often a strong starting point. The right aluminum alloy also depends on temper, shape, and how the part will be fabricated.

What is the difference between 6061 and 7075 aluminum?

6061 is widely used for general fabrication because it offers a good balance of strength, machinability, weldability, and corrosion resistance. 7075 is much stronger but is less suitable for conventional welding. In simple terms, 6061 suits more general-purpose work, while 7075 is often chosen when higher strength is the main priority.