| In the cutting process, there is a cutting metamorphic layer which is obviously different from the material base being formed in the machined surface. Not only are the microstructure of the layer closely related to the surface roughness, hardening and residual stress but also has an important influence on corrosion resistance fatigue resistance and wear resistance.The workpiece material is high strength Aluminum Alloy7050-T7451, and the turning temperature, stress, strain, strain rate and the surface grain size variation are studied at different cutting conditions with the experiments and numerical simulations which focuses on the analysis of the regularity of grain evolution in the metamorphic layer and its influence parameters, and the formation characteristics and corrosion resistance of the surface are studied.Firstly, we researched the formation of cutting force, heat effect mechanism based on the theory of dislocation to clarify the mechanisms of grain refinement and the plasticity condition of refinement formation; According to the characteristics of the dislocation forming of Aluminum Alloy 7050-T7451, the plastic deformation mechanism which influenced by temperature and force in the process is studied, and we selectively analysis the influence of the effects of tool geometry, cutting parameters and cooling conditions on grain refinement during cutting surface.Secondly, we established the DEFORM finite element model which based on J-C constitutive model of Aluminum Alloy 7050-T7451 in cutting condition. Basing on the former research results, we established Aluminum Alloy 7050-T7451 materials turning simulation model, and determined the contact friction parameters between tool and workpiece, heat conduction and convection for heat transfer coefficient. Then we validated the finite element model with the turning experiment about cutting force and cutting heat verification.And through the design of orthogonal turning simulation experiment and single factor turning simulation experiment, the influence of cutting speed, rake angle, cutting radius and turning temperature on t he grain size were explored. The results show that the effect of turning speed on the surface grain size is the most. Also the tool rake angle extrusion effect, edge radius of the plough cut effect, and turning temperature influence on recrystallization are analyzed, and the cutting parameters are optimized.Finally, we studied the turning surface roughness, hardness and microstructure morphology of the Aluminum Alloy 7050-T7451 surface formation characteristics and through the salt spray corrosion experiment, and the effect of surface grain refinement on the corrosion resistance of the workpiece is studied. |
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