<p>The phase distribution, mechanical properties and fracture mechanism of Al-Zn-Mg-Cu alloy with different Mg content after different aging conditions were studied. The results show that the microstructure of the alloys after aging treatment is obviously banded. After the aging treatment, with increasing Mg content, both the size and spacing of η-MgZn₂ precipitates increase, along with a corresponding increase in the area fraction and size of the residual phases, and after RRA treatment, the average grain size of the alloy was reduced. The peak tensile strength (TS) reached after RRA treatment was 597 ± 1.964&#xa0;MPa (2.21 wt%. Mg alloy), 629 ± 2.638&#xa0;MPa (2.76 wt%. Mg alloy) and 632 ± 2.833&#xa0;MPa (3.66 wt%. Mg alloy), respectively. The best overall mechanical performance is RRA + 2.76Mg alloy, because the addition of 2.76 wt%Mg strengthens the material through aging strengthening and fine grain strengthening. The coarse Al₇Cu₂Fe phase is the main reason for the fracture of the alloy, as it tends to cause stress concentration, leading to the formation of micro-crack sources, and ultimately resulting in material fracture. An increase in Mg content leads to an increase in the lamellar Mg (Zn, Cu, Al)₂ phase, which ultimately results in a decrease in the elongation of high Mg alloys.</p> Graphical Abstract <p></p>