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A systematic investigation was conducted to examine the fracture behavior of the structural aluminum alloys 2024, 6061, 7075, and 7178 (in selected heat treatments) tested under several controlled conditions. The investigation included both time independent (tensile, shear, and precracked notch-bend) fractures and time dependent (fatigue and stress corrosion) fractures. Specimens were obtained from both sheet and plate material and tested in longitudinal and transverse orientations. Strain rate effects on fracture morphology were examined in tension and shear tests. Fatigue fracture studies included an examination of the influence of minimum-to-maximum-load ratio on fracture morphology. Second-phase particles observed on fracture surfaces and metallographically prepared sections and corrosion products associated with stress corrosion fractures were analyzed chemically using scanning electron microscopy and energy-dispersive X-ray analysis. Fracture morphology was related to the microstructural features, the testing conditions, and the form of commercial product. The characteristic and distinguishing fracture features were reported for the different alloys. The information obtained from the systematic and controlled studies described here should prove useful in the analysis of service failures that often occur under complex service conditions.
fractures (materials), tensile properties, shear stress, bending, fatigue (materials), stress corrosion, fractography, microstructure, aluminum alloys
Senior metallurgist, Anamet Laboratories, Inc., Berkeley, Calif.
Materials research engineer, NASA Langley Research Center, Hampton, Va.