Influence of corrosion deposits on near-threshold fatigue crack growth behavior in 2xxx and 7xxx series aluminum alloys

The role of corrosion deposits in influencing the near-threshold fatigue crack propagation behavior of 2XXX and 7XXX series aluminum alloys is examined in detail. The composition, thickness, and distribution of fracture surface oxide films are characterized with the aid of X-ray photoelectron spectroscopy, scanning Auger spectroscopy, and secondary ion mass spectroscopy analyses. It is found that the extent of crack closure due to corrosion debris in aluminum alloys is strongly dependent on the composition and aging treatment. The results suggest that environmentally-influenced near-threshold crack propagation in some aluminum alloys is controlled by twoconcurrent andmutually-compctitive mechanistic processes: a dominant role of crack closure due to corrosion deposits (which tends toarrest completely the near-threshold crack) and a strong embrittling effect (which considerablyincreases near-threshold crack growth rates) concomitantly with the crack tip oxidation phenomenon in the moist medium. The near-threshold corrosion fatigue characteristics of aluminum alloys are contrasted with those in a wide range of steels in order to gain an insight into the various

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