Aluminum Alloy Numbering System
Aluminum alloys are categorized using a standardized four-digit numbering system. This system helps engineers, designers, and manufacturers quickly identify the composition, processing behavior, and mechanical properties of a given aluminum alloy.
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.
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:
Series | Main Alloying Element | Characteristics |
1xxx | ≥99% Aluminum | Excellent corrosion resistance, low strength, high conductivity |
2xxx | Copper | High strength, lower corrosion resistance, aerospace applications |
3xxx | Manganese | Good corrosion resistance, moderate strength |
4xxx | Silicon | Good wear resistance, thermal control |
5xxx | Magnesium | Excellent corrosion resistance, marine use, good weldability |
6xxx | Magnesium & Silicon | Versatile, good strength, corrosion resistance, great for extrusion |
7xxx | Zinc | Very high strength, aerospace-grade, sometimes reduced corrosion resistance |
8xxx | Other elements | Specialty uses (lithium, iron, etc.) |
🔸 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.
Alloy Series | Heat-Treatable? | Typical Applications |
1xxx | No | Electrical conductors, decorative use |
3xxx | No | Roofing, cookware, piping |
5xxx | No | Marine structures, pressure vessels |
2xxx | Yes | Aircraft parts, automotive |
6xxx | Yes | Structural components, bicycle frames |
7xxx | Yes | Aerospace, high-stress applications |
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
Why the Alloy Number Matters
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. The numbering system is a universal guide that helps simplify communication between manufacturers, engineers, and procurement teams.
