This study delved into the influence of Mg content on the microstructure and corrosion behavior of homogenized Al-Zn-Mg-Cu alloys. The findings unveiled that alloys featuring a moderate Mg content showcased an exceptionally low immersion corrosion rate of 0.0789   mm/a. A notable 22.3% reduction in average grain size led to a significant 57.2% drop in immersion corrosion rate. Furthermore, the augmentation of the Mg(Zn, Al, Cu)2 phase within the grains contributed to a decrease in the maximum immersion corrosion depth of the alloy. These novel findings offer fresh insights and hold potential for enhancing the corrosion resistance of homogenized Al-Zn-Mg-Cu alloys.