High-Cycle and Ultrahigh-Cycle Fatigue Properties and Failure Mechanism of A380 Aluminum Alloy

Ultrasonic fatigue tests were conducted on A380 aluminum alloy under stress amplitudes of 92‒152 MPa, and the fatigue life distribution of the alloy was studied. With Weibull distribution model and Basquin model, the survival rate-stress amplitude-fatigue life （P-S-N） curves of the alloy at survival rates of 50% and 95% were constructed, and the high-cycle and ultrahigh-cycle fatigue properties and failure characteristics of the alloy were studied. The results show that the stress amplitude-fatigue life of A380 aluminum alloy showed a continuous downward distribution. When the stress amplitude was not less than 128 MPa, most of the samples experienced high-cycle fatigue failure, while a small portion experienced ultrahigh-cycle fatigue failure. When the stress amplitude was lower than 128 MPa, all the samples experienced ultrahigh-cycle fatigue failure. The conditional fatigue strengths for 1×10⁷, 1×10⁸, 1×10⁹ cycles of the alloy at 50% survival rate were 131, 115, 100 MPa, while at 95% survival rate were 110, 97, 85 MPa, respectively. The high-cycle fatigue crack source of A380 aluminum alloy was located on the surface of the sample; there were small cleavage planes and dimple characteristics on the fracture, and the fracture type was quasi-cleavage fracture. The ultrahigh-cycle fatigue failure included fatigue failure with crack source located on the surface and fatigue failure with crack source located inside. The granular bright facet areas and fish-eye area features existed on the fracture of fatigue failure with crack source located inside, and the fatigue fracture was mainly quasi-cleavage fracture. The characteristics fatigue failure with crack source located on the surface were similar to those of high-cycle fatigue failure.