5000 series aluminum alloys are wildly used as high corrosion resistance aluminum alloys for Marine structures. As atmospheric corrosion test, iron powder and artificial sea water were spread on 5083 Aluminum alloy plate. A plate with only artificial sea water was also prepared. And the plates were kept in a humid environment for one week. After testing, pitting corrosion was only observed in plate with iron powder and artificial sea water. However, Fe³⁺ that is stable Fe ion was reported not to effect on corrosion of aluminum alloys.Cations derived from salts such as Na and Mg are investigated in detail as their effect on the corrosion resistance of aluminum alloys. On the other hand, the effect of Fe ions derived from steel materials, which are often used together in structural materials, on aluminum alloys is not clear. So, this study focused on effect of Fe ion on corrosion behavior of 5000 series aluminum alloy.

Then, the effect of Fe ion on the corrosion resistance of aluminum alloys was investigated through electrochemical method in beaker test. Open circuit potential in Fe³⁺ and Cl^- solution was measured. FeCl₃ aq which contained 0.53% Fe³⁺ and 1.0%Cl^- was prepared. Its pH was adjusted to 7.0 with NaOH. NaCl aq (1%Cl^-) was also prepared. OCP of 5083 Aluminum alloy in NaCl aq was -0.8 V vs SCE. However, OCP of FeCl₃ aq was gradually lowered and -1.2V at last. Comparing the surfaces after 500hrs in FeCl₃ aq and NaCl aq, Surface of 5083 Aluminum alloy in FeCl₃ aq showed general corrosion. Surfaces at 0.5 hrs, 30 hrs, and 160 hrs in FeCl3 aq were also observed. The matrix arounds precipitations were dissolved at 0.5hrs. Dissolved area expanded after 30hrs. At last, Discoloration appeared at free surface after 160hrs. Al and O were detected at discoloration area by EDS. It implied that aluminum oxide likely was produced as corrosion product.

Anodic polarization curve in Fe³⁺ and Cl- solution was measured. The anodic polarization curve in FeCl ₃ aq after 0.5hrs was the same as in the NaCl aq.However, OCP lowered after 24hrs. Anode current increment is necessary to lower the OCP. Then, activation of precedence dissolution caused OCP lowering as anodic reaction.Anodic polarization curve in 160 hrs had slightly higher activation potential and lower passivity current than that of 24hrs. So, Al oxide on the surface might possibly protect matrix from corrosion. However OCP kept lower and it did not return to the potential after 0.5hrs.So, the anode reaction was probably kept active even after the oxide was formed on the surface.

Therefore Fe³⁺ ion accelerated anode reaction that caused OCP lowering and corrosion acceleration of 5083 Aluminum alloy.