| As the main medium of microwave transmission in the system, the high quality aluminum rectangular tube is widely used in the field of aviation, aerospace, radar and remote sensing. Due to the specialty of the service environment, the aluminum rectangular tube is required that the shape and dimensional accuracy should be very high, while the inner surface quality must be very good. So the product manufacturing is pretty difficult. The tube with qualified shape and dimensional accuracy can be manufactured with the current research progress by cold drawing. However, the inner surface roughness still cannot meet the design requirements. So it is necessary to analyze the mechanism of surface roughness evolution during plastic deformation to control the surface quality of workpieces. A method combining three dimensional polycrystal finite element calculation with processing tests was used to quantitatively describe the influence of microscopic parameters on the surface roughness evolution based on typical strain path. To explore the surface roughness evolution during plastic deformation, a simple deformation path was chosen in this paper. Because the stress condition during drawing process is so complex, it is not convenient to analyze the influence of individual parameter on the surface roughness.The experiment of cold rolling and recrystallization annealing were carried out first in this paper, to get the trend of microscopic parameters and mechanical properties of Al6061 under different conditions. Then, based on the crystal plasticity theory and mesoscopic finite element model of polycrystalline materials, the method of combining mesoscopic finite element analysis with tensile experiment was used to research the influence of material parameters, such as initial surface roughness, initial grain size and crystallographic orientation on the surface roughness evolution during uniaxial tensile deformation. The main research work are as follows:1) The change of cold-rolled microstructure, texture and mechanical properties of the 6061 aluminum alloy were studied through the cold rolling experiment of hot-rolled sheet with different reduction. The results indicated that with the increase of reduction, the cube texture in hot-rolled sheet decreased for conversion, and the β fiber rolling texture developed. During rolling, the strength and hardness increased, while the elongation decreased gradually.2) The change of recrystallization microstructure, texture and mechanical properties of the alloy were analyzed through the recrystallization annealing of cold-rolled Al6061 sheet with different heating temperature and preservation time. It was found that the average grain size decreased with the increase of reduction. The nucleation rate, the growth rate of nucleus and the driving force for recrystallization increased with the increase of temperature. And the recrystallization was more sufficient to form microstructures with uniform and coarse grains if the preservation time became longer. The cube texture and rotating cube texture with high intensity were formed after annealing. Compared with temperature and reduction, the influence of preservation time on the texture types and distribution was more remarkable. Besides, the strength and hardness decreased when annealing temperature was below the solid solution point. But the ductility increased significantly.3) A 3D polycrystalline material finite element model was established under uniaxial tensile test and the size of mesoscopic analysis model was determined. The results showed that the surface roughness of free surface after stretching increased first with the increase of model size, then tended to be stable. The grains in model with small size deformed heterogeneous during tensile deformation, because there were few grains in the model.4) The model with different initial surface roughness and grain size were adopt for numerical simulation based on uniaxial tension. It turned out that the surface topography after plastic deformation can be approximately divided into two parts: one was the result of heterogeneous deformation(the roughening surface topography), the other was the result of homogeneous deformation(the differential surface topography). The initial surface roughness decelerated the roughening rate(dSq/dε) of the free surface, and the effect of heterogeneous deformation, which caused by misorientation and other factors, on the surface roughness evolution was receded as the initial surface roughness increase. Moreover, grain size in different direction exerted different influence on the surface roughness after deformation.5) The influence of different initial orientation and texture on the surface roughness evolution during tension was studied. Results showed that compared with texture type, the misorientation between grains or the inhomogeneous distribution of crystal orientation were the key factors that lead to surface roughening during plastic deformation.6) The evolution of surface roughness during deformation was researched through the uniaxial tensile test. Compared the results of experiment and numerical simulation, it was found that the trend of surface roughness were basically the same. Therefore, the reliability of mesoscopic analysis model and finite element simulation results were verified.According to the high inner surface quality requirement of aluminum rectangular tube, this work started from carrying out basic experiment, to research on the change of microscopic parameters and mechanical properties of material thoroughly. Then based on the experiment results, a polycrystalline material mesoscopic finite element model was established to analyze the influence of various parameters on the surface roughness evolution during plastic deformation. The research lays a solid foundation for controlling and reducing the inner surface roughness of aluminum rectangular tube after cold drawing in the future. |
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