Aluminum Numbering System

The alloying system for aluminum uses a rational numbering system.  UNS and the Aluminum Association (AA) parallel each other in their numbering system.  For example, AA designates A356.0, UNS uses A13560. 

The UNS system breaks down as follows using A13560 as an example:

First Digit (A)

• An alpha indicator of base metal.  Always A for aluminum.

Second Digit (1)

• Indicates a modification of the original alloy.  Was previously indicated by alpha letter.

Third Digit (3)

• Designates alloy family
  • 1XX 99% Aluminum
  • 2XX Copper
  • 3XX Silicon w/ copper and/or Magnesium
  • 4XX Silicon
  • 5XX Magnesium
  • 6XX Unused
  • 7XX Zinc
  • 8XX Tin
  • 9XX Others

Fourth and Fifth Digits (56)

• Assigned ID number for the particular alloy.

Sixth Digit (0)

• O Casting Specification
• 1 Ingot Specification
• 2 More Tightly Refined Ingot Specification