Research On Microstructure And Mechanical Properties Of Sheet Component During Rotary Forging And Heat Treatment Process

Sheet component is a key main bearing structure widely used in modern aerospace field.The existing manufacturing technology of sheet components is the traditional rolling and extrusion process.Because these two processes are single-freedom-degree plastic forming technology,the final formed sheet components tend to possess obvious anisotropy in their microstructure and mechanical properties,which weakens their service performance and service life.Therefore,in the present study,the multi-degreefreedom rotary forging technology is proposed to manufacture sheet components,so as to effectively control the anisotropy of microstructure and properties.The specific research contents of this paper are as follows:(1)The evolution law of softening annealing microstructure of high-strength aluminum alloy and the effect mechanism of annealing microstructure on roomtemperature plasticity were revealed.The results show that high-strength aluminum alloy softened and annealed at 410 ℃-2h has the highest room-temperature plasticity.The main mechanism is that the annealed structure is the combination of high Schmid factor matrix grains and ellipsoidal second phase,which can coordinate the movement in the forming process,facilitate the migration of deformation dislocations and reduce the degree of deformation stress concentration,leading to the improvement of roomtemperature plasticity.(2)The evolution of microstructure and mechanical properties of 7 sheet component during rotary forging was studied.The results show that when the deformation reduction reaches 70%,the texture and strength of sheet components tend to be isotropic.The main mechanism of texture isotropy is due to the uniform severe circumferential shear strain and the severe lattice rotation in each UFG,isotropic τ-fiber texture get formed;the main mechanism of strength isotropy is due to the continuous isotropic second phase strengthening,grain boundary strengthening and solid solution strengthening,and the isotropic dislocation strengthening,which leads to the final strength isotropy of thin plate members.In addition,when the deformation reduction reaches 70%,a large number of ultrafine grains with the size less than 1 μm get formed.The main mechanism of grain refinement is that the interaction between lattice deflection and dislocation migration leads to the increase of interfacial orientation difference,which promotes the formation of ultrafine grains.(3)The deformation uniformity and fracture failure mechanism of sheet component during rotary forging was studied.During rotary forging,the center layer in core zone of the sheet component possesses most sufficient texture transformation,and the lattice deflection is severe;it also possesses higher degree of "hard texture" segregation which is difficult for slip deformation,so its stress concentration is very intense,which promotes the crack initiation and aggregation in this area,and rapidly expands to other areas,resulting in the overall fracture failure of sheet component.(4)The evolution of microstructure and mechanical properties of sheet component during rotary forging-T6 heat treatment was studied.Compared to the undeformed aluminum sheet material,when the deformation reaches 10%,the heat-treated grains are basically unchanged.The main mechanism is that under this deformation condition,the internal energy storage of matrix grains is small and it is difficult to recrystallize.When the initial deformation reduction is 20%～30%,the final T6 state grains grow abnormally.The main mechanism is that under this deformation condition,the internal energy storage of matrix grains is small and the overall energy gradient of sheet component is small,and only a few areas with relatively larger energy storage get recrystallized first and quickly swallow up the surrounding grains.When the initial deformation reduction is 60%～70%,the final heat treatment grains are uniform and fine.The main mechanism is that the energy storage in the whole aluminum alloy matrix is very large under this deformation condition,and most areas undergo violent recrystallization at the same time,but the grain growth restricts each other leading to the formation of fine equiaxed grains.Compared to the undeformed aluminum sheet material,the strength and plasticity of heat treated sheet component with the deformation reduction of 70% are increased by 7.1% and 80.5%,respectively.The research of this paper has certain theoretical and practical engineering value for establishing the evolution theory of microstructure and mechanical properties of rotary forging of sheet components,developing the control technology of microstructure and properties of rotary forging of sheet components,and promoting the industrial application of rotary forging of sheet components.