The Effects of Grain Distribution on Initiation and Propagation of Fatigue Cracks in 7075-T6Aluminum Alloy Sheet.

摘要

A study was made to determine a mechanism for initiation and propagation of fatigue cracks in 7075-T6 Alclad aluminum alloy sheet specimens subjected to cyclic tensile stresses. Fatigue fracture modes observed with the scanning electron microscope and a light microscope were compared to photomicrographs of polished and etched fracture surfaces of both laboratory and service failures. It was found that fatigue cracks always initiated between grain boundaries of grain fibers which extended to the surface of specimens. Laboratory failures did not exhibit crack morphology similar to that of service failures. It is believed that significant improvements in fatigue resistance could be obtained in specimens having reduced grain size and regular distribution of grain fibers in a direction parallel to the tensile stress direction. (Modified author abstract)