Influence of Cu on microstructure and tensile properties of 7XXX series aluminum alloy

• Copper addtion increases the recrystallization volume fraction of 7XXX alloys.
• The number of precipitated phases rises with the addition of copper.
• Strength and elongation can be enhanced by copper.
• Copper additon plays a key role in turning quasi-cleavage fracture to dimple fracture.

The effect of copper content on tensile properties and microstructure of 7XXX series aluminum alloys at 90% deformation is investigated by tensile test, optical microscopy, scanning electronic microscopy (SEM), X-ray diffraction (XRD) and transmission electron microscopy (TEM). The results show that higher Cu-containing alloy would precipitate more quantity of second-phase particles in rolling process at 420 °C, which facilitates the process of recrystallization during solution treatment. With the increase of copper content from 0 to 1.6 wt.%, the density of ç′ phase and the degree of recrystallization increase, meanwhile the strength and plasticity of Al–Zn–Mg–Cu alloy are improved in T6 heat treatment. In addition, the tensile fracture of Cu-free alloy belongs to quasi-cleavage fracture, while the tensile fracture of Cu-containing alloy is dimple fracture and the number of dimples increases with the increasing of copper content.