The 2xxx series of aluminum alloys are primarily alloyed with copper, which gives them relatively high strength due to solution strengthening and the ability to become harder through precipitation hardening. These alloys typically contain copper in concentrations ranging from 1 to 10%. They naturally age at room temperature, so it’s best to work or form them soon after they’ve been quenched from solution heat treatment. If there’s a delay, it’s advisable to cool them until the mechanical work can be done.
In their fully hardened (age-hardened) state, 2xxx alloys generally have lower ductility compared to some other alloys, and their resistance to atmospheric corrosion isn’t as good as pure aluminum or most non-heat-treatable alloys, except for certain special variations. Without special treatments, 2xxx alloys in the T3 and T4 conditions may be susceptible to stress-corrosion cracking when stressed in the short-transverse direction. Precipitation hardening can enhance resistance to stress-corrosion cracking but reduces ductility and toughness.
Most aluminum-copper alloys are not easily weldable using standard commercial processes, although a few alloys like 2219 and 2195 have been developed specifically for welding applications.