3D Time-Resolved Observations of Fatigue Crack Initiation and Growth from Corrosion Pits in Al 7XXX Alloys Using In Situ Synchrotron X-ray Tomography

In situ three-dimensional X-ray synchrotron tomography was used to visualize and quantify the fatigue crack initiation and growth from corrosion pits in high strength aluminum alloys. Corrosion pitted Al 7075 and Al 7475 samples of peak-aged, over-aged, and highly over-aged conditions were prepared by soaking in 3.5 wt pct NaCl solution for fifteen days. These samples were fatigue tested in situ in 3.5 wt pct NaCl solution using synchrotron X-ray tomography to analyze the fatigue crack initiation and growth characteristics (4D). Increases in maximum pit depth and fatigue crack growth rate variability were found with increased aging. A detailed analysis of crack morphology and deflection, as a function of aging, was carried out and it discussed.