Effects of stress-aging on the microstructure and properties of an aging forming Al–Cu–Mg–Ag alloy

• The initial hardening rate was reduced with external stress during aging.
• Stress-aging can accelerate the precipitation of θ′ but restrain that of Ω.
• Prior deformation can also accelerate the precipitation of θ′ but restrain that of Ω.

The effects of stress-aging on the microstructure and properties of Al–Cu–Mg–Ag alloy were studied by hardness test, electric resistivity test, optical microscopy and transmission electron microscopy. The results show that the application of external stress during aging did not change the grain morphology of Al–Cu–Mg–Ag alloy, but resulted in great changes of the precipitations. The precipitation of θ′ phases was promoted while that of Ω phases was restrained and the initial hardening rate of the alloy decreased. This might originate from the large amounts of dislocations during stress-aging that provided sites facilitating heterogeneous nucleation of θ′ phases. This was verified by the phenomenon that the density of θ′ phases increased while that of Ω phases decreased and the peak hardness was reduced when Al–Cu–Mg–Ag alloy was cold deformed with 6% stretch prior to aging.