Effects of Cu and Al on the crystal structure and composition of η (MgZn) 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 (MgZn) 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. [ABSTRACT FROM AUTHOR]