Aluminum Alloys Naming Convention
Definition of Aluminum Alloy
Aluminum alloys are alloys where aluminum is the predominant material. You will perhaps remember from chemistry that an alloy is a mixture of two metals in a metalic matrix. This mixing of metals into an alloy is done to create a product with unique physical characteristics. Typical alloying elements in aluminum are copper, zinc, manganese, silicon, and magnesium. See chart which describes the composition mixture in various alloys.
The International Alloy Designation System is the most widely accepted naming scheme for wrought alloys. Each alloy is given a four-digit number, where the first digit indicates the major alloying elements.
- 1000 series are essentially pure aluminium with a minimum 99% aluminium content by weight and can be work hardened.
- 2000 series are alloyed with copper, can be precipitation hardened to strengths comparable to steel. Formerly referred to as duralumin, they were once the most common aerospace alloys, but were susceptible to stress corrosion cracking and are increasingly replaced by 7000 series in new designs.
- 3000 series are alloyed with manganese, and can be work-hardened.
- 4000 series are alloyed with silicon. They are also known as silumin.
- 5000 series are alloyed with magnesium, derive most of their strength from work hardening. It is suitable for cryogenic applications and low temperature work. However is susceptible to corrosion above 60°C.
- 6000 series are alloyed with magnesium and silicon, are easy to machine, and can be precipitation hardened, but not to the high strengths that 2000, and 7000 can reach.
- 7000 series are alloyed with zinc, and can be precipitation hardened to the highest strengths of any aluminium alloy.
- 8000 series is a category mainly used for lithium alloys.
The third and fourth digits are significant in the 1xxx series but not in the others. In the 1xxx series the last two digits describe the minimum purity of the aluminium; thus 1145 has a minimum purity of 99.45%; 1200 has a minimum purity of 99.00%. In all other series, the third and fourth digits are simply serial numbers; thus 5082 and 5083 are two distinct aluminium-magnesium alloys. The second digit has a curious function: it indicates a close relationship: thus 5352 is closely related to 5052 and 5252; and 7075 and 7475 differ only slightly in composition.
To these serial numbers are added a suffix indicating the state of hardening or heat treatment (usually indicated with a dash, a letter, and potentially a one to three digit number, e.g. 6061-T6).
The Meaning of the Letter: type of hardening
- F As fabricated
- H Strain hardened (cold worked) with or without thermal treatment
- H1 Strain hardened without thermal treatment
- H2 Strain hardened and partially annealed
- H3 Strain hardened and stabilized by low temperature heating
- HX2 = 1/4 hard
- HX4 = 1/2 hard
- HX6 = 3/4 hard
- HX8 = full hard
- HX9 = extra hard
- O Full soft (annealed
- T Heat treated to produce stable tempers
- T1 Cooled from hot working and naturally aged (at room temperature)
- T2 Cooled from hot working, cold-worked, and naturally aged
- T3 Solution heat treated and cold worked
- T4 Solution heat treated and naturally aged
- T5 Cooled from hot working and artificially aged (at elevated temperature)
- T51 Stress relieved by stretching
- T510 No further straightening after stretching
- T511 Minor straightening after stretching
- T52 Stress relieved by thermal treatment
- T6 Solution heat treated and artificially aged
- T7 Solution heat treated and stabilized
- T8 Solution heat treated, cold worked, and artificially aged
- T9 Solution heat treated, artificially aged, and cold worked
- T10 Cooled from hot working, cold-worked, and artificially age
- W Solution heat treated only.