Comparison of atmospheric corrosion behavior of Al-Mn and Al-Zn-Mg-Cu alloys in a tropical coastal environment

Atmospheric corrosion behavior of 3A21 Al-Mn alloy and 7A09 Al-Zn-Mg-Cu alloy were investigated and compared. Electrochemical results, together with corrosion morphology characterization, suggest that in tropical coastal atmosphere, 3A21 and 7A09 alloys suffer pitting corrosion and intergranular corrosion (IGC), respectively, and 3A21 alloy shows better corrosion resistance and stronger repassivating capability than 7A09 alloy. The pit transition potential E-ptp can be treated as criteria for susceptibility to possible forms of constricted localized corrosion for aluminum alloys. The IGC of 7A09 alloy is mainly caused by the preferential dissolution of the grain boundary precipitates Mg(ZnAlCu)(2), and which results in fast deterioration in the mechanical properties of the field-exposed samples. Besides, morphology and chemical compositions of native oxide layer and corrosion produces layer were characterized by SEM, EDX, and FT-IR analysis, and the corrosion mechanism was also discussed.