• Yb/Zr micro-alloying refines grain size from 232.7 μm to 3.2 μm via pinning of grain boundaries by high-density Al3(Yb, Zr) precipitates.
• Simultaneous improvement of strength and ductility: UTS +16.2%, YS +19.3%, and elongation +112.2% compared to the unmodified alloy.
• Enhanced corrosion resistance due to more discontinuous MgZn2 phase distribution at grain boundaries, retarding intergranular corrosion.
• Provides a cost-effective alloying strategy to overcome the strength-corrosion trade-off in Al-Zn-Mg-Cu alloys.