Effects of the Microstructure of AA 5083 H116 Plate on Its Corrosion Behavior

Intergranular corrosion and exfoliation corrosion tests were conducted on AA 5083 H116 plates of two different thickness. SEM, optical microscopy and 3D imaging system were used to analyze the microstructure. The results show that characteristics of the microstructures, such as grain shape, size and content of β (Mg₂Al₃ or Mg₅Al₈) phase, are different at different depths of the plates. Specimens containing more β phase show high intergranular corrosion susceptibility. After intergranular corrosion test networks of grain boundary were observed at recrystallized surface area where continuous β phase is easy to deposit. Surface area where the β phase content is relatively less and uniformly distributed shows lower intergranular corrosion susceptibility. Directional straight grain boundary resulted from cold deformation could easily lead to deep- going of intergranular corrosion. Area near the surface where the β phase is fine and uniformly distributed shows good exfoliation resistance, and the corrosion goes deeper at the central region where the size β phase becomes relatively larger. Pitting is easy to occur with the increasing size and content of the β phase.