Characterization of Fracture and Fatigue Behavior of 7050 Aluminum Alloy Ultra-thick Plate

The microstructure, mechanical property, fracture toughness, and fatigue behavior of 7050 aluminum alloy pre-stretched ultra-thick plate were investigated by means of optical microscopy, scanning electron microscopy, transmission electron microscopy, tensile test, fracture toughness test, and high-cycle fatigue test. The results showed that the microstructure of the ultra-thick plate consisted of recrystallized grains, subgrains, constituent particles, precipitated phases, and precipitate-free zone. Mechanical tests indicated that anisotropy of fracture toughness existed in L-T, T-L, and S-T orientation. Fractographic features suggested that this anisotropy was significant due to the difference of recrystallized grain on different metallographic planes. Compared to 7050 aluminum alloy plate in less thickness, the ultra-thick plate showed deterioration on fracture toughness due to the increase of recrystallized grains but improvement on fatigue property ascribed to the less densely populated particles. Fractographic observations showed that fatigue initiation of this ultra-thick plate was primarily related to the constituent particles and promoted by increase of the stress amplitude.