The formation and evolution of the Al₈Cu₄Er phase and its influence on the corrosion resistance of Al-Zn-Mg-Er-Sc-Zr alloys were studied by changing the element content of Cu. The results show that with the increase in Cu content, the grains of the alloy are significantly refined, but at the same time, different types of residual phases in the solid-solution-state of the alloy increase. There is a companion relationship between the Al₈Cu₄Er phase and the Al-Fe phase, and they achieve phase transformation through the interaction between Cu and Fe. It can be expressed as the relationship: . The intergranular corrosion of alloys with different compositions shows pitting characteristics closely related to the residual phase. Although the Al-Fe phase containing Cu and Er has a smaller corrosion pit size, the network distribution characteristics increase the corrosion depth, while the Al₈Cu₄Er with better corrosion resistance has a serious decline in the counterpart of the alloy due to its tendency to coarsen and interactive relationship with the Al-Fe phase.