| With the proposal of "Made in China 2025" plan,the demand for low-cost,high-performance materials in the fields of aerospace,automobiles and weapons continues to increase.In this paper,the integrated large strain technology of extrusion and C mode ECA was firstly proposed and the effect of different parameters of the die cavity structure on the processed material was also analyzed.In addition,the Deform-3D finite element analysis was used as a guide to get the optimum mold cavity structure parameters.The shape and structure of the die were designed and the die manufacturing process was developed according to the the existing conditions of the laboratory.The existing extruded 7075 aluminum alloy and autonomous smelted and extruded Al-8.72Zn-2.06 Mg-1.2 Cu-0.218 Zr-0.022 Sr aluminum alloy were used as experimental materials to investigate the regulatory effect of this technology on microstructure and mechanical properties by analyzing the microstructure,mechanical properties and corrosion resistance in different processing stages and directions.The specific research work and related results are as follows.(1)The Deform-3D software was used for numerical simulation and parameter optimization of the integrated large strain technology of extrusion and C mode ECA.The results show that with the increase of extrusion ratio and friction coefficient,and with the decrease of the corner and the outer arc angle of the die,the equivalent strain obtained by the workpiece increases and the maximum extrusion load increases linearly.In addition,an efficient,continuous,and stable integrated large strain processing of extrusion and C mode ECA can be achieved when the extrusion ratio is2,the corner of the die is 120°and the outer arc angle is 60°.(2)The integrated large strain die of extrusion and C mode ECA was successfully designed and manufactured,and the continuous push integrated large strain processing of extrusion and C mode ECA was also successfully carried out.(3)The microstructure,anisotropy and deformation mechanism of 7075 aluminum alloy treated with extrusion and C mode ECA large strain processing andsubsequent heat treatment in different directions of main deformation stages were studied.The results show that after extrusion and C mode ECA large strain treatment,the grain size is refined in all three directions and the degree of grain refinement is Y>X>Z,In addition,the isometry of the grain in the Y direction is improved and there is some anisotropy in crystal orientation and microstructure in different directions.After extrusion and C mode ECA large strain-solution-aging treatment,the elongation of 7075 aluminum alloy increased from 10.17 % to 15.82 %,the elongation increased by 55.59 %.However,the tensile strength decreased by 9.6% and the decrease is mainly due to the decrease of dislocation strengthening,low-angle grain boundary strengthening and aging solid solution strengthening.The hardness of the alloy increased to some extent,the electrical conductivity almost unchanged and both the hardness and electrical conductivity have isotropy.The intergranular corrosion resistance of the alloy in the X and Y direction is decreased but in the Z direction it is almost unchanged.However,the exfoliation corrosion resistance in the X and Y direction is improved but in the Z direction is decreased.The corrosion resistance in different directions of the alloy shows a certain degree of anisotropy.(4)The microstructure,anisotropy and Deformation mechanism of the autonomous smelted and extruded Al-8.72 Zn-2.06 Mg-1.2 Cu-0.218 Zr-0.022 Sr aluminum alloy in different directions of the main deformation stages under extrusion and C mode ECA large strain-solution-aging treatment were studied.The results show that the dynamic recrystallization occurs in all directions after extrusion and C mode ECA large strain-solution treatment and many equiaxed crystals are generated inside the material.The degree of crystallization in the X and Y directions is higher than that in the Z direction.After Deformation treatment,the internal texture of the alloy is improved,The difference in microstructure between the three directions of the alloy is small and the anisotropy of grain is effectively improved.The hardness of the super-strong aluminum alloy changed effectively in all directions after extrusion and C mode ECA large strain-solution-aging treatment.The hardness of the alloy remains unchanged or increased and the anisotropy is not obvious.The conductivity of the alloy did not change significantly in all stages and directions,however,the elongationincreased greatly and reached 21.83%,which is 49.52% higher than the original state.The decrease of strength is mainly due to the decrease of dislocation strengthening low-angle grain boundary strengthening.extrusion and C mode ECA large strain-solution-aging treatment can significantly improve the alloy's resistance to intergranular corrosion and exfoliation corrosion,but it has different effects in different directions.The corrosion ability of the alloy in the X and Y direction is almost the same and the enhance effect in the Z direction is not obvious,which shows a certain degree of anisotropy.In this paper,the large strain technology of extrusion integrated with C mode ECA was creatively proposed and the experiments were conducted using 7075 aluminum alloy and ultra-high strength aluminum alloy as the experimental materials.The experimental results show that this technology can not only effectively refine the grain and regulate the orientation of the crystal,but it can also improve the material's hardness and corrosion resistance to some extent and significantly improve the plasticity. |
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