| China’s new-generation manned rocket to the moon has a take-off thrust of nearly 2700 tons and a carrying capacity of 70 tons in low Earth orbit,nearly three times that of the Long March 5 rocket.Separation ring is the core and key component of inter-stage structure bearing and reliable separation of rocket.The improvement of the performance index of carrier rocket requires it to meet the extreme service performance requirements such as large structural bearing capacity,high-precision assembly and high-reliability separation.The existing inter-stage separation structures and materials in China cannot meet the service requirements.Therefore,in view of the contradiction problem that the bearing capacity and separation function of the separation ring structure have different requirements on the three-way mechanical properties,this paper carried out the research on the precision manufacturing technology of the separation ring extreme service performance.Through the quantitative control of the material characteristic microstructure in various manufacturing links such as forging,ring rolling,deformation heat treatment,etc.A new precise control method of "high temperature multi-direction forging + medium and low temperature rolling deformation + multistage strengthening solution + double stage aging" was proposed for the whole manufacturing process of separation ring,which solved the problems such as the interval control of three-way elongation index of separation ring and the control of the uniformity of microstructure and properties of each part.The high performance manufacturing of the Φ5 m 7050 aluminum alloy separation ring and the application of 7000 series alloy in the rocket separation structure were realized for the first time,which supported the development of a new generation of major space equipment of the manned lunar landing rocket.The main results are as follows.(1)The load bearing and separation function requirements of the interstage separation structure of the new generation manned lunar landing rocket are analyzed,and the extreme service performance index requirements of the separation ring and the problems existing in the high performance manufacturing are put forward.The 7050 aluminum alloy separation ring produced by conventional process has some prominent problems,such as out of limit of axial elongation index(6%),out of limit of annular elongation index(12%),and uneven microstructure and properties of each part.The analysis shows that the coarse deformed fiber structure and mixed crystal inhomogeneous structure are the root causes of the significant difference in the tridirectional elongation of the ring,and the aggregation distribution of residual crystalline phase in the structure is the root cause of the inhomogeneous properties and low local elongation.(2)The influence of forging deformation mode and process parameters on the homogenization refinement and mechanical properties of the residual crystalline phase of 7050 aluminum alloy was studied,and the strategy of controlling the size and distribution morphology of the coarse crystalline phase by multi-direction forging at high temperature was proposed to improve the uniformity of mechanical properties of each part.The mechanical properties of7050 aluminum alloy are closely related to the refinement degree of coarse crystalline phase in the microstructure.The less the content of residual crystalline phase,the more uniform the distribution and the smaller the size,the better the mechanical properties of the material.Increasing the deformation temperature,increasing the deformation amount and decreasing the deformation rate are beneficial to the uniform refinement of the coarse crystalline phase particles.Dissolution diffusion and shear crushing are the main refinement methods.High temperature multi-direction forging can fully dissolve and refine the coarse crystalline phase and improve the uniformity of different parts of the blank.(3)The effect of rolling process on the microstructure and properties of7050 aluminum alloy and the genetic evolution law of grain structure were studied.The strategy of equiaxed grain structure obtained by recrystallization induced by medium-low temperature rolling deformation was put forward to achieve interval control of three-way elongation index.The main deformation mechanism of 7050 aluminum alloy is dynamic recrystallization.Fine equiaxed grain structure can be obtained after forging.At 270℃,the deformation of medium-low temperature rolling is mainly dynamic recovery,while static recrystallization is induced after high temperature solution treatment to obtain equiaxed grain structure,and the recrystallization ratio is 92.9%.A small amount of dynamic recrystallization occurs during high temperature rolling deformation at 460℃.After high temperature solution treatment,the grain structure is a fibrous mixed crystal composed of coarse recrystallized grains and fine subcrystals,and the recrystallization ratio is 60%.The triaxial mechanical properties of the alloy are closely related to the type,morphology and size of the grain structure.The higher the degree of equiaxed grain,the smaller the size,the weaker the fiber direction,the higher the elongation and the smaller the triaxial difference.(4)The influence of process parameters such as solution temperature and holding time,cold deformation,aging temperature and time on the hardening behavior and mechanical properties of 7050 aluminum alloy was studied,and the strategy of graded solution strengthening and double-stage overaging was proposed to realize the coordinated regulation of three-way strength and elongation indexes.By increasing the solution temperature,the strength and elongation of the alloy can be improved simultaneously by promoting the further dissolution and refinement of the coarse residual crystalline phase.The optimal solution temperature is between 477℃ and 482℃.Increasing cold deformation before aging treatment can increase the precipitate density and accelerate the hardening behavior of the alloy,and the optimal cold deformation is 3%.The strength and elongation of 7050 aluminum alloy are significantly different under different peak aging regimes.Double-stage aging is more conducive to the comprehensive regulation of strength and elongation.The three-way tensile and yield strengths of the separation ring gradually decrease with the extension of second-stage aging time,while the elongation basically remains unchanged after increasing to a certain extent.Aging temperature and time are effective means to accurately control the three-way strength and elongation of separation rings.(5)The industrial production of 7050 aluminum alloy Φ5 m separation ring was carried out by the improved new process and passed the ground bearing and separation test verification.Compared with the original process,the recrystallization ratio of the crystal structure of the separation ring produced by the new process is increased from 59.9% to 80.1%,and the equiaxed recrystallization structure is obtained,and the homogeneous refinement effect of the crystalline phase is remarkable.The mean axial and radial elongation of the separation ring increased by 8.4% and 6.6% from 7.4% and 5.7%,respectively,while the tangential direction decreased from 12.6% to 11.1%,and the excess error decreased from 68% to 0,which realized the interval control of the triaxial elongation index.The performance uniformity of each part of the separation ring is significantly improved.In particular,the standard deviation of axial elongation data affecting the separation is reduced from 1.5 to 0.9,which is 40% lower,and the separation reliability is greatly improved.The quality of the 7050 aluminum alloy separation ring produced by the new technology is reliable and has the engineering application conditions,which can meet the development demand of the new generation of manned lunar landing rocket. |
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