The corrosion fatigue behavior of notched 2024-T351 aluminum

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Virginia Polytechnic Institute and State University

Notched tensile tests and notched fatigue tests were performed at room temperature to study the corrosion fatigue behavior of aluminum alloy 2024-T351 in 3% salt solution.

Notched characteristics of aluminum alloy 2024-T351 were found to be the same as those of other high strength aluminum alloys. Triaxiality and stress concentration were the main factors in determination of the notch characteristics. A new definition of notch ductility was developed in this study and the results compared to the use of area-contraction ductility.

Air and 3% salt solution were used as the corrosive agents in the notched fatigue tests. Salt water corrosion was found to decrease the fatigue life to no more than one-fourth of the value for air fatigue. This was explained by the significant effect of salt water which sharpens the notch root rapidly at the early stage of the fatigue tests. However, this fatigue life during salt-water corrosion was decreased by a factor of more than 100 at a stress of 17.1 ksi. This enhanced effect of salt water was found to be the result of rapid propagation of small cracks which would not propagate in air fatigue.

At the nominal stress of 11.4 ksi, notch ductility was found to increase with increasing salt-water corrosion fatigue. This was caused by a tendency for cracks to initiate at the notch root and move parallel to the specimen axis. This surprising result is the only known occurrence of this type of cracking.

The appearance of fractographs obtained by the scanning electron microscope was correlated with the fracture characteristics in both the notched tensile tests and notched fatigue tests.