Elucidation of the trigger for trenching around Al6(Fe, Mn) on AA5083 aluminum alloy in diluted synthetic seawater.

A small area with a large Al 6 (Fe, Mn) particle and a large Mg 2 Si particle was prepared on AA5083, and the dislocation and corrosion behaviors were compared with those of small areas containing only Mg 2 Si and Al 6 (Fe, Mn) particles in 100-times diluted synthetic seawater. Mg 2 Si discolored in both cases upon immersion, but discoloration and trenching were observed for Al 6 (Fe, Mn) only when Mg 2 Si was on the same area. The discoloration of Al 6 (Fe, Mn) started simultaneously with the dissolution of Mg 2 Si. The role of Mg 2 Si in the discoloration of Al 6 (Fe, Mn) particles and the trench formation mechanism was discussed. • Discoloration and trenching occurred for Al 6 (Fe, Mn) only upon Mg 2 Si dissolution. • Alkalization resulting from Mg 2 Si dissolution induced a compositional change on the Al 6 (Fe, Mn) surface. • Oxygen reduction activity on Al 6 (Fe, Mn) significantly increased due to alkalization. • Increased cathodic activity was identified as the cause of trenching around Al 6 (Fe, Mn). [ABSTRACT FROM AUTHOR]