An aluminum callout has two parts. The four-digit number is the alloy, the chemistry. The letters and digits after the dash are the temper, how the metal was worked or heat treated. Both change whether a part bends, welds or machines, so both belong on every order. Five alloys cover most of what small shops buy, and a handful of tempers cover most of those.
The five alloys that cover most orders
6061 is the general-purpose structural and machining alloy. It is heat treatable, usually sold as T6 or T651, machines clean, welds well and anodizes evenly. Its weak spot is forming: 6061-T6 cracks on a tight bend.
5052 is the forming and marine sheet alloy. It gets its strength from cold work, not heat treatment, and is usually sold as H32. It folds tight without cracking, welds well and holds up in salt water. It machines gummy.
3003 is the softest and easiest to form of the common sheet alloys. It shows up in ductwork, trim, tanks and a lot of diamond tread plate. It bends and welds easily but is not strong, and it machines poorly.
7075 is the high-strength machining alloy, close to some steels in strength. It machines beautifully and holds tight tolerances. It is not considered weldable by ordinary arc welding, does not bend, and has lower corrosion resistance than 6061.
6063 is the architectural extrusion alloy. It extrudes into complex shapes with a smooth surface and anodizes well, so it is common in railings, trim, window and door sections and many tube and extrusion profiles. It is weaker than 6061, so it is a poor choice for load-bearing structure.
| Alloy | Best for | Bends? | Welds? | Machines? |
|---|---|---|---|---|
| 6061 | Machined parts, frames, brackets, fixtures | Only with a generous radius in T6 | Yes, with strength loss near the weld | Good |
| 5052 | Formed sheet, boxes, tanks, marine work | Yes, tight bends in H32 | Yes | Fair, gummy |
| 3003 | Trim, ductwork, tread plate, light tanks | Yes, very easily | Yes | Poor, gummy |
| 7075 | High-strength machined parts, tooling | No | Not by standard arc welding | Excellent |
| 6063 | Architectural extrusions, trim, railing | Moderate | Yes | Fair |
General shop behavior. Temper, thickness and bend direction all change the answer on a given part.
Other alloys you will see
2024 is a copper-bearing, high-strength alloy with good fatigue resistance. It is common in aircraft work and some machined parts, usually as T3 or T351. It corrodes more readily than 6061 and is not a good arc-welding candidate.
5086 is a marine plate alloy, stronger than 5052 and very resistant to salt water. Boat builders use it for hulls and decks, often in H32 or H116, a temper made for marine service.
What the temper letters mean
The first letter tells you the basic process. F means as fabricated, with no guaranteed properties. O means annealed, the softest condition. H means strain hardened, strengthened by cold rolling or drawing, and it applies to non-heat-treatable alloys like 3003, 5052 and 5086. T means heat treated, and it applies to heat-treatable alloys like 6061, 6063, 7075 and 2024.
For H tempers, the first digit is the process: H1x is strain hardened only, H3x is strain hardened and then stabilized with low heat so properties do not drift over time. The second digit is how hard: 2 is quarter hard, 4 is half hard, 6 is three-quarter hard and 8 is full hard. So H14 is half hard, H32 is quarter hard and stabilized, and H34 is half hard and stabilized. H112 is material that picked up some hardness from being rolled or extruded, with minimum properties the mill has to meet. You see it on thicker plate and extrusions.
For T tempers, T4 is solution heat treated and aged at room temperature. It is softer than T6 and more formable. T6 is solution heat treated and aged in an oven to full strength. T651 is T6 that has been stretched to relieve internal stress, which is why T651 plate stays flat when you machine one face. T6511 is the same stress relief for extruded bar and shapes, with some minor straightening allowed afterward. T52 is stress relieved by compression and artificially aged, common on 6063 architectural extrusions.
| Temper | What it means | Where you see it |
|---|---|---|
| O | Annealed, fully soft | Parts that get heavy forming before heat treat |
| H14 | Half hard, strain hardened only | 3003 sheet and coil |
| H32 | Quarter hard, stabilized | 5052 and 5086 sheet and plate |
| H34 | Half hard, stabilized | 5052 sheet where more stiffness is wanted |
| H112 | Slightly hardened by rolling or extruding, with minimum properties | Thick 5xxx plate, some extrusions |
| T4 | Solution treated, naturally aged | 6061 that needs moderate forming |
| T6 | Solution treated, artificially aged, full strength | 6061 sheet, bar, tube; 7075 bar |
| T651 | T6 plus stretched for stress relief | 6061 and 7075 plate, rolled bar |
| T6511 | T6 plus stretched, minor straightening allowed | 6061 extruded bar and shapes |
| T52 | Stress relieved by compression, artificially aged | 6063 architectural extrusions |
How to put alloy and temper on an order
Write both, every time: 6061-T651 plate, 5052-H32 sheet, 6063-T52 tube. "Aluminum plate" gets you whatever is quoted first.
If you plan to machine heavily, ask for a stress-relieved temper like T651 or T6511. If you plan to bend, choose the alloy first: 5052 or 3003 before you try to make 6061 behave. If the part is welded and has to carry load, remember 6061 near the weld is weaker than the T6 number on the cert.
Certs list the alloy, temper and tested properties for the lot, and we can include them when you need them. See mill certs for how that works, and the RFQ guide for the rest of what a clean request looks like.