| As the preferred material for structural parts that bears the main force in modern aerospace,the mechanical properties of aviation aluminum alloy show obvious anisotropy due to different rolling,pre-stretch and other forming processes.Under the local large deformation conditions resulted in high-speed machining of "high strain rate,large strain and high temperature",the limitation of the accuracy of material constitutive model reflecting the high-speed cutting conditions results in some limitations in mastering the material deformation mechanism and plastic deformation characteristics.As a consequence,the accuracy of theoretical analysis of high-speed cutting deformation and the reliability of machining simulation is directly affected.In this paper,the pre-stretching rolled plate of aviation aluminum alloy 7050-T7451 is used as research material.By means of theoretical analysis,experimental research and numerical simulation,the dislocation density evolution law of materials under different forming loading directions and angles is analyzed.Then,angle function characterizing the anisotropy of materials and the modified temperature coefficient term is introduced to establish the micro constitutive model under the condition of large cutting deformation.Based on the constitutive model built above,the orthogonal cutting simulation model of aviation aluminum alloy with anisotropic characteristics is established.The mapping relationship between cutting parameters,anisotropy and hardening behavior under high-speed cutting and large deformation condition is revealed,which provides theoretical basis for the research on macro process parameters optimization and micro surface quality of subsequent aviation aluminum alloy processing.Firstly,specimens were obtained along the typical forming directions(ND,TD,RD)and spatial angle directions(RD-30 °-ND、RD-45 °-ND、RD-60 °-ND)of 7050-T7451 aluminum alloy plates.After that,the mechanical properties of aluminum alloy 7050-T7451 were studied by dynamic impact compression test at different strain rates and temperatures.X-Ray Diffraction(XRD)test and Electron Back Scattered Diffraction(EBSD)test were used to explore the dislocation density and its evolution mechanism under the condition of large deformation combined with XRD pattern.Considering the influence of material space forming angle and temperature,the best parameters of constitutive model were obtained based on the mechanical property parameters of different orientations.Using dislocation density model,a modified micro constitutive model with angle function considering the influence of forming direction of material was constructed.Furthermore,the reliability of the constitutive model was verified by comparing the experimental and simulation results.Secondly,the constitutive model was used to reveal the periodic behavior of material hardening at different strain rates and temperatures.The high-speed orthogonal cutting test was carried out on the samples with different forming angles(TD-γ-ND,γ=0°-90°).Based on Oxley cutting theory and cutting inverse method,the anisotropic micro constitutive model of the material under the condition of large deformation cutting was constructed by means of the basic data of shear stress,shear angle,temperature and dynamic mechanical properties of the materials in the deformation zone of high-speed cutting.Thirdly,the finite element simulation of high-speed milling of aluminum alloy7050-T7451 plate was carried out by introducing the anisotropic micro constitutive model,and the mechanism of hardening and plastic deformation was explored.Moreover,the influence law between anisotropy and material hardening behavior was studied by comparing the hardness of cutting surface and the depth of the hardened layer.Furthermore,the mapping relationship between cutting parameters,anisotropy and machinability was revealed.The study obtained above provides data support and theoretical basis for active control of surface quality of aviation aluminum alloy in high-speed cutting. |
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