A series of electrochemical experiments on Al alloys were undertaken to determine their optimum protection potentials in seawater. With 1050 and 5456 alloys, passive films form during anodic polarization but are destroyed by the Cl- in seawater, only to regrow as a result of the self-healing capacity of aluminum. The current density of 5456 Al alloy proved to be lower than that of 1050 as a whole. Any shift to more anodic or cathodic conditions in the potential range of -1.5~-0.68 V resulted in a sudden increase in current density. Current densities in the high-strength 7075 Al alloy showed the greatest values. In contrast, the current densities of 5456 alloy, known to have excellent corrosion resistance in seawater, were the lowest in the range of -0.70~-1.3 V, and we concluded that this potential range offered optimal protection.