The cooling curves of the Al–Zn–In–Mg–Ag alloys in copper mold, iron mold, and 400 °C-preheated iron mold cast were simulated and three solidification rates were calculated to be 7.05 °C/s, 0.76 °C/s, and 0.28 °C/s. The effects of cooling rate on the microstructure, electrochemical characteristics, and corrosion morphologies of Al–Zn–In–Mg–Ag alloys are investigated. The results demonstrate that the alloy with a low cooling rate has the lowest self-corrosion rate (0.09 mm/year), the highest actual capacity (2503.16 Ah/Kg2), as well as the highest anode current efficiency (87.46%). The anode current efficiency of the Al alloys is affected by the self-corrosion and the detachment of the second phases and grains. As the cooling rate decreases, the grain size becomes larger, the amount of the MgZn2 second phase decreases, and the content of In, Zn, and Ag activation elements increases in the matrix. The corrosion of the Al–Zn–In–Mg–Ag alloy initiates from the micro-galvanic corrosion between the MgZn2 second phase and the Al matrix. It then extends along the grain boundaries and towards the intragranular, accompanied by the shedding of the MgZn2 particles and the grains.