Study on Fatigue Properties of Al-Mg Alloy Produced by Severe Plastic Deformation by means of In-Situ SEM Observation

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There have only been a limited number of studies on the fatigue behavior of ultra-fine grained materials with nano- or sub-microcrystalline structure and no reports are available on the fatigue of Equal-Channel Angular Extrusion (ECAE) Al-alloys. The purpose of the present work is to explore cyclic properties of 5056 Al-alloy after ECAE treatment and to get a better insight on general fatigue and tensile performance of materials with fine-grain metastable structures produced by severe deformation. Since the influence of technological parameters on the resultant ECAE structure and properties has not been fully understood yet and is currently being extensively investigated, we do not believe that the results presented here are the best obtainable with the ECAE technology on the Al-alloys. We attempt to clarify both the benefit and draw back of ECAE for fatigue Properties to provide a guideline for further development of this process towards enhancement of practical characteristics of mat … More erials.Mechanical properties and fatigue performance of 5056 A1-Mg alloy fabricated by the ECAE are assessed in tensile and cyclic experiments in terms of yield stress, ultimate tensile strength, elongation, fatigue limit, S-N curve and fatigue growth rate.1) The modest enhancement of fatigue performance is achieved in the high stress regime in the fine-grain 5056 A1-Mg alloy if compared with the conventional O-temper material having a relatively large grain size. This advantage is, however, to a large extent discredited by a higher crack growth rate at low and intermediate stresses, lower apparent fatigue threshold and lower thermal stability of the severely predeformed alloy.2) The ECAE technique, in its form Used for the present work, does not reveal a distinct advantage for high-cyclic fatigue when compared with standard processing. Although this result may look discouraging, there is an obvious enhancement of the fatigue life in the low cyclic regime and of the crack growth rate at large stress intensity factor range. Additionally we have to bear in mind that the flexibility to vary many parameters during equal-channel pressing provides perspective possibilities for microstructure control and, therefore, for materials design. Further development of ECAE processing is necessary to improve fatigue and/or tensile performance of ECAE Al-alloys. Less