Durability of the AMg6 alloy under consequtive dynamic and vhcf of loading in a corrosive environment

Abstract

The paper describes an experimental methodology developed for very-high-cycle fatigue testing (number of cycles 10 8-109) of dynamically pre-loaded specimens made of aluminum alloy AMg6. The preloading modes ensured the occurrence of controlled damage, which made it possible to simulate structural changes in the material of fan blades under conditions of high- speed collision with solid particles. The specimens were preloaded by dynamic stretching of specimens on a split Hopkinson pressure bar at strain rates up to ~10 3 c-1 followed by ultra-high- cycle loading on a Shimadzu USF-2000 ultrasonic testing machine. This allowed specimen testing during 10 8-1010 cycles with amplitudes up to several tens of micrometers and test frequency of 20 kHz under conditions of enhanced cooling with compressed air and salt mist (3%NaCl). The study of fracture surfaces by the fractographic method showed that for this number of loading cycles, the role of the external environment increases significantly, which, in particular, means that the sea salt fog is one of the most aggressive external factors for aircraft. Based on the profilometry data (interferometer-profilometer New-View 5010 with a resolution of 0,1 nm), quantitative correlations have been established between the mechanical properties and scale-invariant characteristics of the relief of fracture surfaces formed in the processes of dynamic and gigacycle loading.