| Due to its special physical and chemical properties,magnesium alloy has become an engineering structural material with extremely high development potential,and is widely used in aviation,aerospace,transportation and other fields.In real life,structural materials are bound to serve in cyclic load loading environment,but the strong basal texture of traditional magnesium alloy makes it asymmetrical in tension and compression,reducing its fatigue life.The rare earth magnesium alloy can weaken the basal texture and improve its fatigue performance.The microstructure of a material determines its macroscopic mechanical properties.Therefore,a scientific and comprehensive understanding of the evolution of the microstructure of the rare earth magnesium alloy during fatigue deformation is not only a prerequisite for studying its fatigue damage mechanism,but also the basis for the development of a new type of high fatigue life magnesium alloy.It is highly academic and practical significance.In this paper,pure Mg and Mg-3Y alloy ingots were used as raw materials,through suitable rolling annealing process,so that the two had the same grain size(10-15?m).Through SEM,EBSD quasi-in-situ characterization of both at 1% strain control LCF.The evolution process of microstructure and structure under cyclic fatigue was caught.Combining the analysis methods of slip traces and twin variants,the activation law of the microscopic plastic deformation mechanism under the low cycle fatigue and the similarities and differences of the corresponding fracture modes were studied.The effects of Y addition on the low cycle fatigue behavior of Mg were summarized.Studies have shown that:1.After 1% tensile loading in the first week,pure Mg and Mg-3Y both activated basal plane slip as the main deformation mechanism with a small amount of {10-12}stretching twins.But Mg-3Y activated basal slip slightly more,corresponding to the lower tensile yield strength;After 1% compression load in the first week,Mg-3Y activated more base slip and {10-12} tensile twins,and deetwinning occurs where the twins were formed,corresponding to its higher compressive yield strength,while pure Mg slip and twinning increase were limited;2.After 1% strain control low cycle fatigue failure,the content of pure Mg {10-12}tensile twins is 2.3 times that of Mg-3Y,but the amount of base surface slip is only 53.4%of Mg-3Y,which is almost inactive non-basal slip,and 19.8% of Mg-3Y slip is non-base surface slip.During low-cycle fatigue,pure Mg was dominated by {10-12} tensile twin deformation,while Mg-3Y was dominated by dislocation slip,some of which were non-basal slip;3.Almost all of the {10-12} tensile twins of pure Mg were produced in the compression loading stage,the variants were randomly selected,but their c-axis was mainly distributed in the range of TD to RD30 °,while Mg-3Y twinning occurred both in the stretching and compression stages,and the c axis of the variant was randomly distributed on the circumference of the {0001} pole figure TD-RD;4.Mg-3Y grains were more prone to slip transmission to coordinate deformation,and pure Mg was more likely to form twin chains.Pure Mg was mainly intergranular fracture,and there were a certain number of transgranular fractures,while almost all of Mg-3Y was intergranular fracture.Due to the single deformation mode of pure Mg,the deformation of each grain is uneven,and transcrystalline fractures occur along the PSB and twin boundaries;while the Mg-3Y deformation modes are diverse,the deformation within and between the grains is coordinated,and basically no transgranular fractures occur.5.The addition of Y not only weakens the texture of the base surface,but also reduces the value of CRSSnon-basal / CRSSbasal,promotes the opening of the base surface slip and non-base surface slip and the transfer of slip,and the deformation of each grain is more uniform,reducing the occurrence of cracks makes Mg-3Y have better low-cycle fatigue performance. |
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