Investigation of the elevated-temperature low-cycle fatigue failure mechanism of 2024-T3 aluminum alloy

Abstract:

To elucidate the elevated-temperature fatigue failure behavior of lightweight aluminum alloy drill pipe materials in deep drilling， axial tension-compression stress-controlled fatigue tests were conducted on 2024-T3 aluminum alloy at 120， 160， and 200 °C with stress amplitudes of 200， 250， and 300 MPa. The failure mechanisms were analyzed via stress-strain hysteretic response， scanning electron microscopy fracture morphology， and backscattered electron imaging. The results show that fatigue life decreases markedly with increasing stress amplitude， which is the primary factor controlling life attenuation. The influence of temperature exhibits significant stress amplitude dependence； at intermediate and low stress amplitudes of 200 and 250 MPa， the fatigue life at 200 °C shows a recovery compared with that at 160 °C， whereas at a high stress amplitude of 300 MPa， it declines continuously with rising temperature. Analysis of the hysteretic response reveals that cyclic plastic deformation is enhanced at 160 °C， resulting in increased macroscopic inelastic energy dissipation. However， at 200 °C， the hysteresis loop area does not expand continuously， indicating a discrepancy between macroscopic dissipated energy and local fatigue damage， with the dominant failure mechanism shifting from uniform plastic dissipation to localized strain concentration and particle-matrix interface damage. Observations of fracture morphology indicate that crack propagation is dominated by stable fatigue striations at low temperatures and low stress amplitudes. Elevated temperatures and high stress amplitudes lead to rougher fracture surfaces with increased secondary cracks， dimples， tear ridges， and particle pull-out features. Backscattered electron imaging confirms that Cu-enriched coarse second-phase particles serve as critical microscopic damage sources for crack initiation and propagation. It is concluded that the fatigue failure is jointly governed by matrix thermal softening， cyclic plastic deformation， and particle-matrix interface damage. Under high-temperature and high-stress-amplitude conditions， interface decohesion and microvoid coalescence accelerate crack propagation and reduce fatigue life. The findings provide experimental support and a theoretical basis for service reliability evaluation of lightweight aluminum alloy drill pipe in ultra-deep wells.