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The Effect of Microstructure on Intergranular Corrosion Resistance of 6061 Alloy Extrusion

Intergranular corrosion (IGC) behavior of 6061 aluminum alloy extrusions was investigated. After IGC test in accordance with ISO/DIS 11846 (method B), heavy IGC was observed and the corrosion reached about 300 μm deep from the surface. However, it became clear that the IGC did not propagate more than 300 μm deep from the surface during IGC test for a long period. It was considered that the IGC was caused by the existence of PFZs because PFZs were clearly observed on the surface layer of the extrusion but were not observed in the center position of the extrusion thickness. Furthermore, it was considered that the formation of PFZs was associated with the grain boundaries characteristics. That is, it was suggested that most of the grain boundaries had random high angle in the surface layer of the extrusion, but had small angle in the center plane of the thickness. To verify this hypothesis, the center plane which was cold rolled and recrystallized was examined by the IGC test. As a result, heavy IGC was observed because the center plane had random high angle boundaries and PFZs.