Extremely low cycle fatigue behaviour of high strength 2024-T351 aluminum alloy

článek ve sborníku ve WoS nebo Scopus

en

It has been found in recent years that the conventional Manson-Coffin law tends to overestimate the fatigue life at high levels of plastic loading. Such reduction in fatigue life is associated with a fundamental change in the mechanism of damage accumulation. Deterioration of the structure by cracks propagation becomes marginal and the fatigue resistance is governed by the ductility exhaustion phenomenon. The plastic deformation ability under extremely low cycle fatigue conditions is generally related to the occurrence of secondary phases, ie. inclusions and precipitates, dispersed in the matrix. This study investigates the microstructure of hardenable 2024 aluminum alloy and its effect on the cyclic response in the extremely low cycle fatigue region. Metallographic samples of the studied alloy were probed using SEM/EDS and EBSD analysis to identify the morphology and chemical composition of the observed phases. Fatigue tests were conducted in a symmetrical push-pull regime under strain control at room temperature and cyclic plasticity and S-N curves were determined. Electron microscopy observations revealed anisotropic microstructure with numerous fragmented inclusions. Fractographic analysis showed that these hard and brittle secondary phases act as an effective microstructural flaw leading to strong plastic damage accumulation and subsequently to fatigue cracks nucleation. In terms of fatigue life curves, a huge discrepancy in the fatigue data was observed at the extreme levels of cyclic straining. To overcome this shortcoming, a new three-parameter regression function was successfully employed and the obtained results were further discussed.

It has been found in recent years that the conventional Manson-Coffin law tends to overestimate the fatigue life at high levels of plastic loading. Such reduction in fatigue life is associated with a fundamental change in the mechanism of damage accumulation. Deterioration of the structure by cracks propagation becomes marginal and the fatigue resistance is governed by the ductility exhaustion phenomenon. The plastic deformation ability under extremely low cycle fatigue conditions is generally related to the occurrence of secondary phases, ie. inclusions and precipitates, dispersed in the matrix. This study investigates the microstructure of hardenable 2024 aluminum alloy and its effect on the cyclic response in the extremely low cycle fatigue region. Metallographic samples of the studied alloy were probed using SEM/EDS and EBSD analysis to identify the morphology and chemical composition of the observed phases. Fatigue tests were conducted in a symmetrical push-pull regime under strain control at room temperature and cyclic plasticity and S-N curves were determined. Electron microscopy observations revealed anisotropic microstructure with numerous fragmented inclusions. Fractographic analysis showed that these hard and brittle secondary phases act as an effective microstructural flaw leading to strong plastic damage accumulation and subsequently to fatigue cracks nucleation. In terms of fatigue life curves, a huge discrepancy in the fatigue data was observed at the extreme levels of cyclic straining. To overcome this shortcoming, a new three-parameter regression function was successfully employed and the obtained results were further discussed.

Aluminum alloy 2024, inclusions, cyclic plasticity, low cycle fatigue, regression functions

30.06.2022

TANGER Ltd.

Ostrava

978-80-88365-06-8

31st International Conference on Metallurgy and Materials, METAL 2022

714–720

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