ACCUMULATION OF MICROSTRUCTURAL DAMAGE DUE TO FATIGUE OF HIGH-STRENGTH ALUMINUM-ALLOYS

The microstructural features of aluminum alloy 7050-T7451 in the vicin ity of fatigue cracks and on the crack path were studied to determine which of these features influence fatigue crack propagation. The studi es included characterization of the full spectrum of microstructural a nd fracture surface features-from the largest (e.g., roughness and gra in type) to the smallest (e.g., second-phase particles and dislocation s). Of all the features studied, only the second-phase particles were shown to have a definite influence by causing crack deflection. The nu mber of particles encountered by the fatigue cracks were significantly higher than the expected average. The fatigue crack path was predomin ately transgranular, and there was no change in the dislocation and pr ecipitation structures in the crack-affected zone.