Alloy Identification and Designations
AlCuMg2 is the German wrought-alloy designation for the heat-treatable Al-Cu-Mg family registered as 2024 in the Aluminium Association system and as 2A12 in the Chinese GB system. Copper is the principal strengthening element, magnesium provides the age-hardening response, and manganese controls grain structure and limits strength loss at moderately elevated temperature. The grade is a classic high-strength hard aluminium: it is soft enough to be formed in the annealed condition and then hardened by solution treatment plus natural or artificial ageing. It is routinely stocked as extruded round, square and hexagonal rod, as rolled plate, and as drawn or extruded tube.
Registered Chemical Composition
Composition limits for the AlCuMg2 / 2024 / 2A12 grade, as registered in GB/T 3190 and consistent with the ranges published in EN 573-3, are given below in mass percent.
| Element | Limit (wt%) | Function |
|---|---|---|
| Cu | 3.8 - 4.9 | Primary strengthener |
| Mg | 1.2 - 1.8 | Age-hardening response |
| Mn | 0.30 - 0.9 | Grain control, hot strength |
| Si | 0.50 max | Impurity control |
| Fe | 0.50 max | Impurity control |
| Zn | 0.30 max | Impurity control |
| Ti | 0.15 max | Cast grain refinement |
| Ni | 0.10 max | Impurity control |
| Others | 0.05 each, 0.15 total | Residual limits |
| Al | Balance | Matrix |
Mechanical Properties by Product Form
In the T351 / T4 temper, bar and rod produced to ASTM B211 is specified with a minimum tensile strength of 470 MPa (68 ksi) and a minimum yield strength of 325 MPa (47 ksi) over the common small-diameter range. Rolled plate to ASTM B209 carries the same 470 MPa / 325 MPa minima for T351, tested in the longitudinal direction. In the annealed O temper the product is deliberately soft, with typical tensile strength below 250 MPa, which is why forming and bending are carried out before final heat treatment rather than after it. Properties are verified on tension specimens tested to ASTM E8.
Heat Treatment Practice
Solution treatment is carried out at 495-505 degrees C followed by a water quench; artificial ageing is then performed at 185-195 degrees C for 6-12 hours and air cooled. Where natural ageing is used instead, full properties develop after approximately 96 hours at room temperature. Quenching rate is the critical variable: slow quenching, or quenching of thick sections with low surface-to-volume ratio, promotes intergranular attack and reduces the corrosion performance of the finished part even when tensile results still comply.
Forms, Sizes and Applicable Specifications
Extruded bar and profile are supplied to ASTM B221, drawn seamless tube to ASTM B210, extruded tube to ASTM B241 and rolled plate to ASTM B209. Straightness, diameter tolerance and length tolerance follow the dimensional tables of the relevant specification, and tensile property requirements are taken from the same document so that form and property verification stay consistent. Rod is commonly supplied in the size range where the specified longitudinal properties are demonstrated on specimens taken from sections up to 22 mm across.
Corrosion, Machining and Joining
Atmospheric corrosion resistance is moderate and the alloy is usually anodised, painted, or protected by a metallurgically bonded layer of 1xxx-purity aluminium on the finished surface. Spot welding behaviour is good, but gas and argon arc welding tend to produce intergranular cracking in the heat-affected zone, so welded assemblies are normally redesigned for mechanical fastening or riveting. Machinability is good in the cold-worked and aged condition and poor in the annealed state, which makes final machining a post-ageing operation.
Typical Applications
Typical uses include aircraft structural fittings, rivets, hydraulic manifolds, truck and trailer frames, moulds, jigs and high-load machine components where the strength-to-weight ratio of 2024-class material is required and service temperatures stay below roughly 120 degrees C.
Frequently Asked Questions
Q: Is AICuMg2 the same alloy as 2024 and 2A12?
A: Yes. AlCuMg2 is the older German designation, 2024 is the Aluminium Association registration, and 2A12 is the GB registration; the three share the same copper and magnesium ranges listed in the composition table.
Q: What minimum strength should be expected in the T351 temper?
A: Bar, rod and plate are specified with a minimum tensile strength of 470 MPa (68 ksi) and a minimum yield strength of 325 MPa (47 ksi) when tested longitudinally to the requirements of ASTM B211 or ASTM B209.
Q: Why does the alloy need anodising or cladding?
A: Because its corrosion resistance in the uncoated condition is only moderate, so anodic films, paint systems or a bonded high-purity aluminium surface layer are used to protect the finished component in outdoor and marine-adjacent service.
Q: Can the rod and plate be welded without cracking?
A: Gas and argon arc welding carry a real risk of intergranular cracking in the heat-affected zone; resistance spot welding performs well, and where fusion welding is unavoidable the joint design and filler selection must be qualified by mechanical testing.
Q: Which tempers are normally supplied?
A: O for forming, and T351 or T4 for components that need full strength; T6-type artificial ageing is used where dimensional stability at slightly elevated service temperature matters more than peak ductility.
Q: How should the material be machined?
A: Machine after ageing, not in the annealed state. The aged temper gives clean chip formation and good surface finish, while the soft O temper tears and produces poor finishes.