| 7055 aluminum alloy is widely used in aerospace and other important fields because of its good performance.The 7055 aluminum alloy prepared by traditional casting method has coarse structure,low density and unstable performance,which restricts its use.In recent years,the 7055 aluminum alloy produced by the spray forming method has attracted more and more attention because of its fine grain,dense structure and stable performance.However,such alloys are prone to produce large residual stresses during the heat treatment process,which causes the components to deform and crack during subsequent machining,which seriously affects their service life.Therefore,for the residual stress of 7055 aluminum alloy in spray forming,this paper uses finite element simulation to analyze the evolution of residual stress during quenching and aging of the alloy,and uses the contour method to measure the residual stress to verify the simulation results.At the same time,through tensile experiments to analyze the evolution of alloy properties under different heat treatment processes,combined with TEM technology to analyze the evolution of alloy structure,summarize the mechanism of alloy performance differences according to the evolution of the structure.Finally,the structural analysis and characterization of the cracks that occurred during the heat treatment of the alloy components were analyzed,the cracking mechanism was analyzed,and related optimization processes were formulated to reduce the occurrence of fracture behavior.The research results show that the spray-formed 7055 aluminum alloy reaches peak aging at 120°C/24 h single-stage aging.Among them,the alloy after quenching at 20°C has a yield strength of 692 MPa,an elongation of 10.8%,and after 80°C The quenched alloy has a yield strength of 680 MPa and an elongation of 11.6%.The alloy’s strong shape in the peak aging state is well matched,the overall performance is excellent,and the increase in the quenching temperature of the alloy’s performance is not greatly reduced.TEM analysis results show that with the increase of aging temperature in the single-stage aging state,the size of the intragranular precipitation phase of the alloy gradually grows,from the initial small round particles to gradually grow into elongated rods with a slightly larger size.For round particles,the grain boundary precipitation phase gradually changes from the initial continuous state to a discontinuous state,and the noprecipitation zone at the grain boundary gradually widens.When the two-stage aging temperature is raised to 160°C,the alloy reaches the peak aging state at 120°C/8h+160°C/2h.Among them,the alloy after quenching at 20°C has a yield strength of 703 MPa and an elongation of 9.0% The alloy after quenching at 80°C has a yield strength of 699 MPa and an elongation of 9.1%.The performance of the two-stage aging alloy is significantly improved in the early stage of aging,and then the performance drops rapidly.After the alloy undergoes two-stage aging heat treatment,a high-density precipitate phase is formed in the crystal.At the same time,the size of the precipitate phase is slightly increased compared with the single-stage aging state,and the precipitate phase has obvious orientation distribution characteristics,and the grain boundary phase size is increased.Large,enhanced discontinuity,no widening of precipitation zone.Thermal compression experiments were carried out on the 7055 aluminum alloy formed by spray forming,and the constitutive equation of the alloy was constructed.The quenching stress of the alloy was simulated using the obtained constitutive equation.After quenching,the residual stress was symmetrical in the thickness direction of the thick plate Distribution,the surface layer is divided into compressive stress,and the central part is distributed as tensile stress.When quenched at 20°C,the maximum compressive stress of the surface layer is-232 MPa,and the maximum tensile stress of the core is 210 MPa.When the quenching temperature is increased to 80°C,the stress level drops significantly.At this time,the maximum compressive stress of the surface layer is-127 MPa,and the maximum tensile stress of the core is 139 MPa.The results show that increasing the quenching temperature can significantly reduce the residual stress level of the alloy.Creep experiments were carried out on the alloy to construct the creep constitutive equation of the alloy to simulate the evolution of the residual stress during the aging process.The simulation results show that the stress level of the alloy after 120°C / 24 h single-stage aging treatment has decreased significantly.The stress of the core of the component after quenching at 20°C has been reduced by about 20%,and the surface stress has been reduced by about 15%.After 80 The core stress of the quenched component at°C is reduced by about 28%,and the surface stress is reduced by about 30%.The stress level of the alloy under the two-stage aging is also significantly reduced,but compared with the single-stage aging,the stress level is not much different.The measurement results using the profile method show that the error between the simulation results and the measurement results is within 15%,and the simulation results can be considered accurate and reliable.The problem of quenching cracking of components is analyzed.The analysis results show that the main reasons for cracking of quenched components are concentrated in two aspects:(1)grain boundary weakening/brittleness caused by overheating/overburning and stress concentration effects,which are inherent in quenching cracking The cause;(2)local strong tensile stress during quenching,which is the external cause of local quenching cracking.The quenching of large-sized components of different structures and the simulation of residual stress during aging found that the residual stress concentration is not obvious when the U-groove is opened,the tendency of the alloy to crack is small,and when the U-groove is not open,it shows that A relatively large tensile stress is formed,and cracking easily occurs during processing.The simulation results of the aging process show that aging can effectively reduce the stress of the alloy after quenching,which is beneficial to the subsequent machining process. |
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