Aluminium Grades Chart

The aluminium alloy series

Four digits identify a wrought alloy. The first is the series and tells you the main alloying element; the rest identify the specific alloy within it. A temper code follows the grade, such as 6061-T6, and describes the heat treatment.

Common grades compared

These are the grades that come up in general fabrication. Yield figures are for the temper listed and drop sharply in the annealed condition.

Marine aluminium grades

The 5xxx series is the marine series because magnesium gives it a stable oxide layer that resists chlorides, and because it does not rely on heat treatment for strength, so welding does not create a soft zone.

5083 is the boatbuilding standard for hulls and structure. 5052 is the lighter-duty choice for fittings, tanks and trim. Both are supplied in the H116 or H321 tempers for marine work, which are stabilised against the stress corrosion cracking that can affect high-magnesium alloys after long exposure to warm salt water.

6061 and 6082 are acceptable for above-waterline structure and fittings that stay dry, but they pit if left in salt water and the heat-affected zone of a weld loses roughly a third of its strength. 7075 has no place in a marine environment.

Aluminium hardness

Aluminium hardness is quoted on the Brinell scale with a 500 kg load, and the range is wide. Pure 1100-O is around 23 HB and dents with a fingernail; 7075-T6 is around 150 HB, close to a mild steel.

The temper matters more than the grade for hardness. 6061 goes from about 30 HB annealed to 95 HB in T6. If a part has to resist wear or hold a thread, specify the temper, not just the alloy.