Aluminum Alloy Numbering System: Complete Decoding

Have you ever seen an aluminum part stamped with a code like “6061” or “7075” and wondered what those numbers mean? They’re not random. Aluminum alloys are categorized using a standardized four-digit numbering system, called aluminum alloy numbering system. This system helps engineers, designers, and manufacturers quickly identify the composition, processing behavior, and mechanical properties of a given aluminum alloy.

This guide will decode the aluminum alloy numbering system for you, digit by digit, so you can make informed decisions.

At AMSpec, we specialize in producing high-precision aluminum extrusions and drawn tubes, and we work closely with our clients to recommend the most suitable alloy and temper for their performance needs.

How the Aluminum Alloy Numbering System Works

The aluminum alloy numbering system, primarily developed by the Aluminum Association (AA), assigns four-digit codes to identify different alloy families. These numbers indicate the main alloying element and help distinguish between wrought alloys and casting alloys.

Decoding the 4-Digit System: Wrought Aluminum Alloys (for extrusion, rolling, forging, drawing)

Wrought aluminum alloys use a four-digit code, where each digit holds specific information:

🔸 First Digit: Major Alloying Element

Indicates the primary alloying element, which largely defines the alloy series:

🔸 Second Digit: Alloy Modification

• 0 means original alloy in the series.
• 1–9 indicates a variation or modification of the original alloy.

🔸 Third & Fourth Digits: Specific Alloy Identifier

These digits further distinguish the alloy but do not follow a specific pattern. They are assigned in the order the alloys are registered.

Heat-Treatable vs Non-Heat-Treatable Alloys

Understanding whether an alloy can be strengthened by heat treatment or only by cold working is essential for choosing the correct process path.

Key Takeaways When Reading Alloy Numbers

• • First digit = Primary alloying element
  • Second digit = Modification to the original alloy
  • Last two digits = Identify specific alloy or indicate purity level (for 1xxx series)
  • Alloy number + temper (e.g., 6061-T6, 7075-T73) = Complete material designation

Putting It All Together: An Example

Let’s break down one of the most common alloys, 6061-T6:

• 6xxx: The principal alloying elements are Magnesium & Silicon.
• x0xx: It is the original alloy in this formulation.
• xx61: This is its unique identifier.
• -T6: This is the temper designation, indicating it has been solution heat-treated and artificially aged to a high-strength condition.

Why the Aluminum Alloy Numbering System Matters for Your Project

Choosing the correct alloy series helps ensure:

• • Optimal strength-to-weight ratio
  • Suitable corrosion resistance
  • Machinability and formability
  • Compatibility with welding or anodizing
  • Cost-effectiveness for production

Choosing the Right Aluminum Alloy

Choosing the correct alloy is not just about strength—factors like corrosion resistance, thermal conductivity, weldability, and formability are equally important. aluminum alloy numbering system is a universal guide that helps simplify communication between manufacturers, engineers, and procurement teams.

Need help navigating the world of aluminum alloys? The engineering team at AMSpec is here to help you select the perfect alloy and temper to meet your performance, quality, and budget requirements. Contact us today to discuss your project.

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