| The defense industry,aerospace and other high-tech fields have a strong demand for lightweight equipment.Al-Zn-Mg-Cu alloy cabins with high strength and high strength can meet the requirements of high strength,toughness and lightweight load-bearing components of equipment.In this paper,based on the manufacturing requirements of high-strength and tough Al-Zn-Mg-Cu alloy rocket projectile flight stabilization device,the coarse insoluble phase and mechanical properties of components were coordinated by upsetting extrusion pre-deformation and extrusion forming combined with heat treatment.The influence of upsetting extrusion pre-deformation and extrusion on refining of insoluble phase and its mechanism were studied.A new method of large plastic deformation was developed which combines the upsetting extrusion pre-deformation and the insoluble phases control of extrusion forming.The effect of solution process on the solubility behavior of insoluble phase and mechanical properties of components was also studied.The microstructure of aluminum alloy cabins meeting the requirements of ultra-high strength performance was clarified.The controlling mechanism and method of insoluble phase of Al-Zn-Mg-Cu alloy were obtained.It provides theoretical value and engineering technology basis for exploring the strengthening and toughening mechanism of high-Zn-aluminum alloy components and manufacturing of high-strength and toughening Al-Zn-Mg-Cu alloy cabins.The main conclusions of this paper are as follows:1.The upsetting extrusion pre-deformation and extrusion test results show that the upsetting extrusion pre-deformation of the billet before extrusion contributes to the elimination of the insoluble phase of Al-Zn-Mg-Cu alloy,and its mechanism is as follows:During the large plastic deformation process of upsetting extrusion pre-deformation,the maximum tangential stress produces severe shearing effect on the grain and the second phase,resulting in grain refinement and formation of new grain boundaries.At the same time,with the second phase breaking and dispersion distribution,it has a higher solid solubility in high temperature solution condition,promotes the increase of aging precipitated phase quantity,and finally improves the strong plasticity of the material.The best heat treatment process of sample grade extruded bar formed at 450℃ and 430℃ is solution at 480℃ and aging at120℃.The tensile strength,yield strength and elongation are 795 MPa,773MPa and 7.9%,respectively.2.The effect of solution temperature on the insoluble phase of Al-Zn-Mg-Cu alloy cabin is greater than that of solution time.Although the multistage solution process can make the limit solution temperature higher than the multi-phase eutectic temperature through the solution treatment of gradual warming,which can improve the recirculation degree of the insoluble phase（residual insoluble phase accounts for 2.25%-2.62%）and reduce the ablation phenomenon of the second phase,but it can’t be stably eliminated.However,475℃×3h is the best solution process with high recirculation degree of insoluble phase and no ablative phenomenon,and the proportion of residual insoluble phase is 2.63%.120℃×24h single-stage aging is the best aging process coupled with 475℃×3h single-stage solution process.When the aging time is 24 h,the volume fraction of precipitated phase reaches 99.5%,and the main precipitated phase is η ’phase,and the component has peak mechanical properties.Therefore,the optimal heat treatment process of Al-Zn-Mg-Cu alloy cabin is 475℃×3h solution +120℃×24h aging.The best mechanical properties are tensile strength of 715.0mpa,yield strength of 695 MPa and elongation of 7.5%.3.By analyzing the microstructure of the extruded and heat-treated samples of the cabin,it is found that the microstructure of the alloy has a high recrystallization level,which is the main way to obtain fine grain of the alloy.The main strengthening mechanisms of al-Zn-Mg-Cu alloy cabin during forming and heat treatment are precipitation strengthening mechanism,fine grain strengthening mechanism and dislocation strengthening mechanism. |
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