Study On Low Cycle Fatigue Behavior Of 7075 Aluminum Alloy Gradient Microstructure

Light alloys are widely used in aerospace and military fields due to their good comprehensive properties.In order to avoid the loss of engineering components caused by operating under alternating load conditions,the fatigue behavior of light alloy gradient microstructures has become a popular research topic.However,most of the gradient structures in the existing research are gradient structures prepared by surface strengthening.In this paper,the purpose of this paper is to study the low-cycle fatigue behavior of the overall gradient structure formed by uneven deformation.At the same time,two different grain sizes were studied.low cycle fatigue properties.Using extruded 7075 aluminum alloy as raw material,the microstructure and texture before deformation and the fracture morphology after deformation are analyzed by scanning electron microscope,and the connection between its microstructure and macroscopic properties is finally established,which provides theoretical support for fatigue life prediction.and data references.Research indicates:The stronger texture strength of the coarse grain sample will lead to higher yield strength and higher tensile strength of the coarse grain sample than the fine grain sample in the quasi-static tensile properties.At the same time,the texture strength of the graded samples is lower,which will lead to lower yield strength and tensile strength than the coarse grain samples.Therefore,the texture strength will have a larger contribution than the grain refinement strengthening.For the fatigue experiments of two different grain sizes,under low strain,the fatigue life of coarse grain is lower than that of fine-grained structure;under high strain,the fatigue life of coarse grain is higher than that of fine grain.For the fatigue experiments of gradient microstructure,the fatigue life of gradient microstructure is lower than that of coarse grain microstructure at low strain;the fatigue life of gradient microstructure is higher than that of coarse grain microstructure at high strain.Therefore,the fatigue life of coarse grain and fine grain is non-positively related to their quasi-static properties at low strains;the opposite is true at high strains.The fatigue life of graded and coarse grain is non-positively related to their quasi-static properties at high strains;the opposite is true at low strains.A continuous dynamic recrystallization phenomenon is proposed in the fine grain.During the extrusion deformation process,a small-angle grain boundary dominated by the longitudinal direction is first generated in the original grain,and the small-angle grain boundary gradually turns into a large-angle grain boundary.,so as to form new grains;when the width of the new grains is about 5 ?m,when the deformation continues,lateral small-angle grain boundaries will be generated inside the grains,which will gradually rotate to form large-angle grain boundaries.Die further separated.One of the recrystallization rules of extruded 7075 aluminum alloy is that when the matrix is oriented in the <111> direction,the recrystallization in the <001> direction is more likely to occur,and when the matrix is oriented in the <001> direction,the <111> direction is more likely to occur.Recrystallization;one of the typical recrystallization laws of the equiaxed and elliptical regions after torsional deformation is that when the matrix is oriented in the <111> direction,the recrystallization in the <111> direction is more likely to occur;the same recrystallization law as the extruded 7075 aluminum alloy is produced.Low-cycle fatigue fracture behavior Under low strain,the fatigue striation spacing of the coarse grain is 0.9 ?m,and the fatigue striation spacing of the fine grain is 0.7 ?m in the crack propagation zone of two different grain size structures.Under high strain,the fatigue striation spacing of the coarse grain in the crack propagation zone is 2.0 ?m,and no fatigue striation is found in the fine grain.In the gradient structure fatigue fracture,the fatigue striation spacing in the crack propagation zone under low strain is as small as 0.3 ?m.At the same time,the crack propagation zone area is smaller than that of the coarse grain structure and fine grain fracture.Under high strain,the gradient structure in the crack propagation zone has a smaller fatigue striation spacing of 0.6 ?m compared with the coarse grain.