What do the numbers on aluminum mean?

The numbers on aluminum represent different alloys within the aluminum family. The Aluminum Association has assigned a four-digit numerical designation to each alloy, which provides information about the alloy composition and properties.

The first digit indicates the major alloying element or group of elements present in the alloy. For example, the 1xxx series alloys (e.g., 1100, 1050) are pure aluminum with a minimum aluminum content of 99%, while the 6xxx series (e.g., 6061, 6063) contain magnesium and silicon as the main alloying elements.

The remaining three digits provide more specific information about the alloy composition, variations, and modifications. These digits help differentiate between different alloys within the same series and indicate specific properties such as strength, formability, and corrosion resistance.