| Large aluminum alloy monolithic thin-walled components are key structural components of air and space launch equipment,which have complex shape and structure and high performance requirements,and therefore are difficult to be formed and manufactured.Creep aging forming provides a new way to integrate the shape and properties of large thinwalled components through coupling the creep and aging strengthening characteristics of aluminum alloys with thermal energy fields.However,the aluminum alloy will undergo a long period of natural aging after solution quenching,which will change the initial tissue state of the billet and affect the subsequent creep behavior and aging precipitation strength,and then affect the forming accuracy and performance consistency of the component,which is one of the key problems in the application of creep aging forming technology in aluminum alloy components.Therefore,in this paper,for the 2A14 aluminum alloy with significant natural aging,creep aging experiments,mechanical tensile properties,XRD,TEM and other tests were carried out under different pretreatment and forming process conditions to investigate the influence law of two pretreatment regimes,natural aging and pre-deformation,on the creep aging behavior of2A14 aluminum alloy,to match different pretreatment regimes with creep aging process,and to further establish the Finally,the accuracy of the intrinsic structure model and the feasibility of the matching process were verified by finite element simulation and trial fabrication of flat parts.The conclusions of this paper are shown as follows:(1)The creep aging experiments of 2A14 aluminum alloy under different natural aging time(NA0h,NA3 d,NA2w,NA3m)and different pre-deformation(0%,4%,8%)were carried out,and through mechanical tensile,XRD,TEM and other tests,it was found that the natural aging effect of 2A14 aluminum alloy is significant,and the shorter natural aging time can increase the creep amount of the alloy in subsequent creep aging by a small amount,and the creep amount of the alloy in natural aging for more than The creep amount of the alloy with natural aging for more than3 days tends to be stable.As natural aging proceeds,the size of θ’ phase does not change significantly after creep aging,but the ratio of the number of θ’ and Q’ phases in the alloy changes,and the percentage of θ’ phase increases from 18% to 22%.The pre-deformation can weaken the natural aging effect of the alloy,and the creep amount of the pre-deformed alloy hardly changes with natural aging.The dislocations introduced by predeformation promote the precipitation of θ’ phase,and the larger the predeformation,the higher the percentage of θ’ phase in the alloy and the slightly larger the size,which makes the creep amount and strength of the alloy increase.(2)Based on the evolution of the morphology of the alloys with different pretreatment regimes(0%-NA0 h,0%-NA2 w,4%-NA2w)at different temperatures(150°C,160°C,170°C),the suitable matching processes for different pretreatment alloys were determined: the best matching temperature for 0%-NA0 h and 0%-NA2 w pretreatment alloys was 160°C,and the peak aging time was 12-16 h.The best matching temperature for 4%-NA2 w pretreatment alloy is 160°C and the peak aging time is 8-16 h.The differences in creep and mechanical properties of T34-state 2A14 aluminum alloy at different process parameters were investigated.The results show that the increase in temperature and applied stresses intensifies the movement of precipitated phases and dislocations in the alloy and promotes the growth of the precipitated θ’ phase in the alloy,which results in an increase in the strength of the alloy.the stress index of the alloy at 160°C is 1.03,indicating that the creep mechanism is grain boundary diffusion.In the range of 150-170°C,the apparent activation energy is calculated to be 80.4 k J/mol,indicating that the diffusion mechanism of the alloy is dominated by grain boundary diffusion.The low performance of the alloy in the early creep aging period is due to the fact that there is almost no Q’ phase in the alloy at this time,and only a small amount of fine θ^’ phase is nucleated and precipitated on the dislocation.(3)A unified macro and micro intrinsic model of creep aging of 2A14 aluminum alloy under different pretreatment regimes was established,and the parameters in the model were solved by particle swarm algorithm(PSO)to fit the creep amount,yield strength,shape factor,relative volume fraction,precipitation phase length and relative dislocation density,respectively.The relative errors of the experimental and fitted values were5.8703%,1.6139%,2.4615%,1.5756%,2.6597%,and 0.4873%,respectively,with high fitting accuracy.(4)Two different pretreatment regimes(0% pre-deformation and 4%pre-deformation)were carried out to simulate the finite element creep aging forming of 2A14 aluminum alloy flat parts,and the accuracy of the simulation model was verified through the trial production of flat parts.the relative errors of the predicted radii of the two types of flat parts were 9.77%and 9.69%,respectively,and the deviations of the shape surface were within ±1 mm. |
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