Correlation between corrosion behavior and grain boundary characteristics of a 6061 Al alloy by lab-scale X-ray diffraction contrast tomography (DCT)

In this work, the corrosion behavior of a peak aged 6061 Al alloy was investigated through a combination of x-ray tomography and lab-scale x-ray diffraction contrast tomography (DCT). Pitting corrosion and intergranular corrosion (IGC) were both observed when the alloy was immersed in a 3.5 wt% NaCl solution. Pitting corrosion happens at the position of both Al5FeSi inclusions and Mg2Si precipitates. The intergranular corrosion is actually caused by the galvanic cell between grain boundary precipitates and the matrix. The 3D distribution of grain boundary characteristics was quantitatively analyzed by DCT and correlated with the IGC behavior. Investigations revealed that grain boundaries with misorientation angles smaller than 25° or larger than 45° exhibited stronger resistance to IGC. Grain boundaries with misorientation between 25° and 45° corroded more easily. The influences of IGC on the tensile properties and fracture mechanisms were also elucidated in this work.