It is the third and fourth digits, indicating the aluminum content.
2-8 is the third and fourth digits, which has no special meaning and is only used to distinguish other alloys.
Aluminum is divided into pure aluminum, hard aluminum, super hard aluminum, antirust aluminum and forged aluminum.
- 1 series pure aluminum has the most aluminum content, reaching more than 90%
- 2-Series hard aluminum alloy, containing copper and Cu, with high hardness
- 3-Series antirust aluminum alloy, containing manganese and Mn, with good corrosion resistance
- 5-series antirust aluminum alloy, manganese Mn, magnesium mg, low density and high tensile strength
- 6-series forged aluminium alloy, magnesium mg, silicon Si, malleable (bending)
- 7-series superhard aluminum alloy, zinc containing Zn, Mg, Cu, copper, high hardness and high strength