Effects of Cu and Al on the crystal structure and composition of η (MgZn2) phase in over-aged Al–Zn–Mg–Cu alloys

Heat treatable Al–Zn–Mg alloys can be strengthened by the precipitation of second phase particles. In this paper, Al–6.57%Zn–2.83%Mg and Al–6.57%Zn–2.83%Mg–3.92%Cu alloys (in wt%) in T7 state (140 °C for 96 h) have been prepared. The effects of Cu and Al on the concentration and structure of equilibrium η (MgZn2) phase have been investigated by high resolution transmission electron microscopy, aberration-corrected scanning transmission electron microscopy, selected election diffraction pattern simulations, and first-principles calculations. The effects of Cu and Al substitution on the diffraction characteristics of the η phase and the general rule of Cu and Al substitution in the η phase have been discussed.