The Wrought Alloy Designation System is a coding system used to identify alloys and consists of four digits, occasionally preceded by a capital letter. The first digit signifies the primary alloying elements. The second digit indicates the alloy’s variation, while the last two digits specify the exact alloy designation. ANSI H35.1/H35.1M Defines this system.
For example: 6061
Digit 1
Assigning the first digit of an alloy designation is usually straightforward unless there’s an equal mix of two or more alloys. In such cases, there’s a specific order to follow: copper (Cu), manganese (Mn), silicon (Si), magnesium (Mg), magnesium silicide (Mg2Si), and zinc (Zn). For instance, if a new alloy contains equal amounts of manganese and zinc, it’s assigned to the 3xxx series. The 6xxx series requires more judgment because alloys with more silicon than magnesium, but significant quantities of both, tend to be placed in the 6xxx series for properties and characteristics, due to the dominance of the magnesium and silicon combination.
Main alloying elements
- 1xxx Mostly pure aluminum; no major alloying additions
- 2xxx Copper
- 3xxx Manganese
- 4xxx Silicon
- 5xxx Magnesium
- 6xxx Magnesium and silicon
- 7xxx Zinc
- 8xxx Other elements (e.g., iron and silicon)
- 9xxx Unassigned
Digit 2
The second digit in an alloy designation reflects variations in a specific alloy, often involving tighter control of impurities to achieve specific properties. If it’s 0, it means the alloy is mostly pure aluminum with natural impurities. When the second digit is between 1 and 9, it indicates special control over impurity levels or adjustments to major alloy elements to achieve desired performance.
Digits 3 & 4
In the 1xxx series, the last two digits represent the purity level, with the first two digits indicating the aluminum purity in percentage terms. For example, 1060 means it contains a minimum of 99.60% aluminum.
In the 2xxx to 8xxx series, the last two digits don’t have any special meaning. They’re used only to distinguish individual alloys and don’t reflect the order of development or registration. Historically, for older alloys, these digits were based on earlier designations (e.g., 2024 was 24S before 1950). In recent times, developers of new alloys choose specific numbers, often based on proximity to other alloys or ease of memorization. For instance, Alloy 2020, which is no longer in use, was named this way for convenience. If a developer requests a specific number for registration, the Aluminum Association Product Standards Committee, which oversees the system, usually approves it if it doesn’t cause confusion. However, if no preference is indicated, the committee typically assigns the lowest available number from 1 to 99.
References
Introduction to Aluminum Alloys and TempersJ. Gilbert Kaufman, p23-37
ANSI H35.1/H35.1M-2017 – American National Standard Alloy And Temper Designation Systems For Aluminum