Abstract
It is difficult to evaluate the corrosion pit using normal observation methods because of the complex shape of the pit and its passive film. In this study, measurements of pit and crack formation in corrosion fatigue tests of high-strength aluminum alloy, 7075-T651 were conducted by synchrotron radiation CT imaging. 3D/4D analysis was applied to the observation of corrosion pit growth and crack initiation in corrosion fatigue tests. Pits and inclusions were recognized individually in 3D/4D analysis. The corrosion pits showed complex shapes, and parts of pits grew under the surface of specimens along inclusions. It was found that the behavior of the corrosion pit under the surface was affected by the inclusions distribution. The stress intensity factor range ΔK was calculated based on the measured shape and dimensions of the corrosion pit. The value of ΔK increased with increasing loading cycles, and the value of ΔK at the location of crack initiation indicated larger than 0.9 MPa m1/2, which was similar to the threshold stress intensity factor range ΔKth for corrosion fatigue of A7075-T651.
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