The constitutive modeling and springback simulation for AA2524 sheet in creep age forming（CAF） process were presented.A series of creep aging tests were performed on AA2524 at the temperature of 180-200 °C and ...The constitutive modeling and springback simulation for AA2524 sheet in creep age forming（CAF） process were presented.A series of creep aging tests were performed on AA2524 at the temperature of 180-200 °C and under the stress of 140-210 MPa for 16 h.Based on these experimental data,material constitutive equations which can well characterize creep aging behaviors of the tested alloy were developed.The effect of interior stress distributed along the sheet thickness on springback was simulated using FE software MSC.MARC by compiling the established constitutive models into the user subroutine.The simulation results showed that the amount of sheet springback was 61.12% when merely considering tensile stress existing along the sheet thickness;while sheet springback was up to 65.93% when taking both tensile and compressive stresses into account.In addition,an AA2524 rectangular sheet was subjected to CAF experiment in resistance furnace.The springback value of the formed rectangular sheet was 68.2%,which was much closer to 65.93%.This confirms that both tensile and compressive stresses across the sheet thickness should be considered in accurately predicting springback of the sheet after forming,which can be more consistent with experimental results.展开更多
Creep aging behavior of retrogression and re-aged(RRAed)7150 aluminum alloy(AA7150)was systematically investigated using the creep aging experiments,mechanical properties tests,electrical conductivity tests and transm...Creep aging behavior of retrogression and re-aged(RRAed)7150 aluminum alloy(AA7150)was systematically investigated using the creep aging experiments,mechanical properties tests,electrical conductivity tests and transmission electron microscope(TEM)observations.Creep aging results show that the steady-state creep mechanism of RRAed alloys is mainly dislocation climb(stress exponent≈5.8),which is insensitive to the grain interior and boundary precipitates.However,the total creep deformation increases over the re-aging time.In addition,the yield strength and tensile strength of the four RRAed samples are essentially the same after creep aging at 140℃ for 16 h,but the elongation decreases slightly with the re-aging time.What’s more,the retrogression and re-aging treatment are beneficial to increase the hardness and electrical conductivity of the creep-aged 7150 aluminum alloy.It can be concluded that the retrogression and re-aging treatment before creep aging forming process can improve the microstructure within grain and at grain boundary,forming efficiency and comprehensive performance of mechanical properties and electrical conductivity of 7150 aluminum alloy.展开更多
Creep age forming(CAF)is an advanced forming technology that combines creep deformation and age hardening processes.When compared with the conventional forming technologies including roll bending and shot-peen forming...Creep age forming(CAF)is an advanced forming technology that combines creep deformation and age hardening processes.When compared with the conventional forming technologies including roll bending and shot-peen forming,CAF has many advantages of low residual stress,excellent dimensional stability,good service performance and short production cycle.It is an optimal technique for precise manufacturing for shape and properties of large-scale complicated thinwalled components of light-weight and high strength aluminum alloys in the aviation and aerospace industries.Nevertheless,CAF has an inevitable disadvantage that a large amount of springback occurs after unloading,which brings a challenge on the accurate shape forming and property tailoring of components.Therefore,how to achieve accurate prediction and control of springback has always been a bottleneck hindering the development of CAF to more industrial applications.After the factors of affecting springback and measures of reducing springback are summarized from the internal and external aspects,constitutive models for predicting springback and springback compensation methods for CAF of aluminum alloy panel components are reviewed.Then,a review of research progresses on tool design for CAF is presented.Finally,in view of the key issue that it is difficult to predict and control the shape and properties of components during CAF,the technical challenges are discussed and future development trends of CAF are prospected.展开更多
In order to investigate the springback rules, the variation characteristics of physical property and microstructure in bending creep age forming process, a series of creep forming tests of 2124 aluminum alloy were con...In order to investigate the springback rules, the variation characteristics of physical property and microstructure in bending creep age forming process, a series of creep forming tests of 2124 aluminum alloy were conducted based on three kinds of single and double curvature forming tools. The results show that the spingback rate would be the minimum under the optimal coupling conditions among the temperature, aging time and internal stress state of material. Difference exists in the two directions of the formed sample with double curvature, but the curvature variation keeps the same. Yield strength, ultimate tensile strength and fracture toughness of the double curvature formed sample appear to be higher than those of the single curvature formed sample under the same aging condition, but the elongation and the anisotropy are opposite.展开更多
The bending deformation method was adopted to characterize the creep deformation behavior of Al-Cu-Li alloy in the creep aging forming(CAF) process based on a series of CAF tests, and the evolution laws of its mechani...The bending deformation method was adopted to characterize the creep deformation behavior of Al-Cu-Li alloy in the creep aging forming(CAF) process based on a series of CAF tests, and the evolution laws of its mechanical properties and microstructures under different pre-deformation conditions were studied. The results show that the bending creep strain characterization method can intuitively describe the creep variation. With the increase of the pre-deformation strain, the creep strain of the specimen firstly increases and then decreases. The increase of the pre-deformation strain can promote the course of aging precipitation, and improve the formed alloy’s tensile properties at room temperature, the Kahn tearing properties, and the fatigue propagation properties. Pre-rolled specimens produce a slightly weaker work hardening than pre-stretched specimens, but they also create a stronger aging-strengthening effect;thus the strength, toughness and damage performance can be improved to some extent. Among all the types of specimens, the specimen with 3% rolling after CAF treatment has the best comprehensive mechanical properties.展开更多
Non-isothermal Creep Age Forming(CAF),including loading,heating,holding,cooling and springback stages,is an advanced forming technique for manufacturing high performance large integral panels at short production perio...Non-isothermal Creep Age Forming(CAF),including loading,heating,holding,cooling and springback stages,is an advanced forming technique for manufacturing high performance large integral panels at short production period and low cost.However,the creep deformation and aging precipitation during heating stage is often neglected in experiments and modeling,leading to low forming precision.To achieve shape forming and property tailoring simultaneously,a deep understanding of the non-isothermal creep aging behavior and the establishment of predictive models are urgently required.A new five-stage creep feature of Al-Cu-Li alloy during the non-isothermal creep aging is observed.The microstructural interactions between the dislocations,solute atoms,Guinier Preston zones(GP zones)and T1 precipitates are found to dominate the five-stage creep aging behavior.The physical-based model considering temperature evolution history is established to describe the five-stage creep feature.The springback and yield strength of non-isothermal creep age formed plates with different thicknesses are predicted and compared by non-isothermal CAF experiments and corresponding simulations.The CAF experiments show that the springback and yield strength of the non-isothermal creep age formed plate are 62.1%and 506 MPa,respectively.Simulation results are in good agreement with experimental results.The proposed model broadens the application of traditional CAF models that mainly focus on isothermal conditions.展开更多
Hot stretch-creep forming （SCF） is a novel technique to produce hard-to-form thin-walled metal components. Comprehensively considering the analysis results of the springback angle, yield strength and microstructure,...Hot stretch-creep forming （SCF） is a novel technique to produce hard-to-form thin-walled metal components. Comprehensively considering the analysis results of the springback angle, yield strength and microstructure, four hot SCF process parameters including temperature, stretch velocity, post stretch percentage and dwelling time of a Ti-6Al-4V alloy sheet were optimized using an orthogonal experiment. The results reveal that temperature is the most important factor on springback angle. The yield strength of the deformed material in 0° direction increases, while those in directions of 45° and 90° fluctuate around the original value. After hot SCF, the shape of some a phases changes from short thin grains to long slender ones, and the microhardness changes very little. The optimized parameters with temperature of 700 ℃, stretch velocity of 5 mm/min, post stretch percentage of 2% and dwelling time of 8 min are achieved finally.展开更多
Creep ageing forming(CAF)has been widely used in the aerospace engineering,but how to optimize the processing conditions,especially under complex stress state of the CAF process for large-size components produced by f...Creep ageing forming(CAF)has been widely used in the aerospace engineering,but how to optimize the processing conditions,especially under complex stress state of the CAF process for large-size components produced by friction-stir welding is still a great challenge to now.In this work,the creep ageing behaviors and underlying microstructure evolution of a thick friction-stir welded Al-Cu alloy plate after CAF process under different stress levels are systematically investigated.The creep strain and the strength of the joint are both significantly increased when the stress is close to the average yield strength of the initial weld joint.The grain size reduces while the local strain and dislocation density increase from top to bottom of the NZ;hence,the bottom layer of the weld joint exhibits higher creep strain and steady-stage creep strain rate during the CAF process.The results reveal that the gradient microstructures sensitive to the stress level effectively govern the creep-ageing performance from the upper to the bottom layer in a thick friction stir welded Al-Cu alloy plate.Rationally increasing the initial dislocation density of the weld joint can both enhance the tensile properties and promote the creep deformation of the weld joint for CAF process.展开更多
A unified constitutive model is presented to predict the recently observed“multi-stage”creep behavior of Al−Li−S4 alloy.The corresponding microstructural variables related to the yield strength and creep deformation...A unified constitutive model is presented to predict the recently observed“multi-stage”creep behavior of Al−Li−S4 alloy.The corresponding microstructural variables related to the yield strength and creep deformation of the alloy during the creep ageing process,including dislocations and multiple precipitates,have been characterized in detail by X-ray diffraction(XRD)and transmission electron microscopy(TEM).For the yield strength,the model considers the multiphase strengthening behavior of the alloy based on strengthening mechanisms,which includes shearable T1 precipitate strengthening,non-shearable T1 precipitate strengthening andθ′precipitate strengthening.Based on creep deformation mechanism,the“multi-stage”creep behavior of the alloy is predicted by introducing the effects of interacting microstructural variables,including the radius of multiple precipitates,dislocation density and solute concentration,into the creep stress−strain model.It is concluded that the results calculated by the model are in a good agreement with the experimental data,which validates the proposed model.展开更多
The effect of temperature in range of 155-175 ℃ on the creep behavior, microstructural evolution, and precipitation of an Al-Cu-Li alloy was experimentally investigated during creep ageing deformation under 180 MPa f...The effect of temperature in range of 155-175 ℃ on the creep behavior, microstructural evolution, and precipitation of an Al-Cu-Li alloy was experimentally investigated during creep ageing deformation under 180 MPa for 20 h. Increasing temperature resulted in a noteworthy change in creep ageing behaviour, including a variation in creep curves, an improvement in creep rate during early creep ageing, and an increased creep strain. Tensile tests indicate that the specimen aged at higher temperature reached peak strength within a shorter time. Transmission electron microscopy(TEM) was employed to explore the effect of temperature on the microstructural evolution of the AA2198 during creep ageing deformation. Many larger dislocations and even tangled dislocation structures were observed in the sample aged at higher temperature. The number of T1 precipitates increased at higher ageing temperature at the same ageing time. Based on the analysed results, a new mechanism, considering the combined effects of the formation of larger dislocation structures induced by higher temperature and diffusion of solute atoms towards these larger or tangled dislocations, was proposed to explain the effect of temperature on microstructural evolution and creep behaviour.展开更多
基金Project(2014CB046602)supported by the National Basic Research Program of ChinaProject(20120162110003)supported by Ph D Programs Foundation of Ministry of Education of China
文摘The constitutive modeling and springback simulation for AA2524 sheet in creep age forming（CAF） process were presented.A series of creep aging tests were performed on AA2524 at the temperature of 180-200 °C and under the stress of 140-210 MPa for 16 h.Based on these experimental data,material constitutive equations which can well characterize creep aging behaviors of the tested alloy were developed.The effect of interior stress distributed along the sheet thickness on springback was simulated using FE software MSC.MARC by compiling the established constitutive models into the user subroutine.The simulation results showed that the amount of sheet springback was 61.12% when merely considering tensile stress existing along the sheet thickness;while sheet springback was up to 65.93% when taking both tensile and compressive stresses into account.In addition,an AA2524 rectangular sheet was subjected to CAF experiment in resistance furnace.The springback value of the formed rectangular sheet was 68.2%,which was much closer to 65.93%.This confirms that both tensile and compressive stresses across the sheet thickness should be considered in accurately predicting springback of the sheet after forming,which can be more consistent with experimental results.
基金Project(2017YFB0306300)supported by the National Key Research and Development Program of ChinaProject(2017ZX04005001)supported by the National Science and Technology Major Project,China+2 种基金Project(JCKY2014203A001)supported by National Defense Program of ChinaProjects(51905551,51675538,51601060)supported by the National Natural Science Foundation of ChinaProjects(Kfkt2018-03,zzYJKT2019-11)supported by State Key Laboratory of High-Performance Complex Manufacturing,China。
文摘Creep aging behavior of retrogression and re-aged(RRAed)7150 aluminum alloy(AA7150)was systematically investigated using the creep aging experiments,mechanical properties tests,electrical conductivity tests and transmission electron microscope(TEM)observations.Creep aging results show that the steady-state creep mechanism of RRAed alloys is mainly dislocation climb(stress exponent≈5.8),which is insensitive to the grain interior and boundary precipitates.However,the total creep deformation increases over the re-aging time.In addition,the yield strength and tensile strength of the four RRAed samples are essentially the same after creep aging at 140℃ for 16 h,but the elongation decreases slightly with the re-aging time.What’s more,the retrogression and re-aging treatment are beneficial to increase the hardness and electrical conductivity of the creep-aged 7150 aluminum alloy.It can be concluded that the retrogression and re-aging treatment before creep aging forming process can improve the microstructure within grain and at grain boundary,forming efficiency and comprehensive performance of mechanical properties and electrical conductivity of 7150 aluminum alloy.
基金financial support from the Key Program of the National Natural Science Foundation of China (No.51235010)the National Science Fund for Excellent Young Scholars (No.51522509)the National Natural Science Foundation of China (NO.51905424)
文摘Creep age forming(CAF)is an advanced forming technology that combines creep deformation and age hardening processes.When compared with the conventional forming technologies including roll bending and shot-peen forming,CAF has many advantages of low residual stress,excellent dimensional stability,good service performance and short production cycle.It is an optimal technique for precise manufacturing for shape and properties of large-scale complicated thinwalled components of light-weight and high strength aluminum alloys in the aviation and aerospace industries.Nevertheless,CAF has an inevitable disadvantage that a large amount of springback occurs after unloading,which brings a challenge on the accurate shape forming and property tailoring of components.Therefore,how to achieve accurate prediction and control of springback has always been a bottleneck hindering the development of CAF to more industrial applications.After the factors of affecting springback and measures of reducing springback are summarized from the internal and external aspects,constitutive models for predicting springback and springback compensation methods for CAF of aluminum alloy panel components are reviewed.Then,a review of research progresses on tool design for CAF is presented.Finally,in view of the key issue that it is difficult to predict and control the shape and properties of components during CAF,the technical challenges are discussed and future development trends of CAF are prospected.
基金Project(2010CB731700)supported by the National Basic Research Program of China
文摘In order to investigate the springback rules, the variation characteristics of physical property and microstructure in bending creep age forming process, a series of creep forming tests of 2124 aluminum alloy were conducted based on three kinds of single and double curvature forming tools. The results show that the spingback rate would be the minimum under the optimal coupling conditions among the temperature, aging time and internal stress state of material. Difference exists in the two directions of the formed sample with double curvature, but the curvature variation keeps the same. Yield strength, ultimate tensile strength and fracture toughness of the double curvature formed sample appear to be higher than those of the single curvature formed sample under the same aging condition, but the elongation and the anisotropy are opposite.
基金Project(2017YFB0306301)supported by the National Key Research and Development Program of ChinaProject(51705539)supported by the National Natural Science Foundation of China。
文摘The bending deformation method was adopted to characterize the creep deformation behavior of Al-Cu-Li alloy in the creep aging forming(CAF) process based on a series of CAF tests, and the evolution laws of its mechanical properties and microstructures under different pre-deformation conditions were studied. The results show that the bending creep strain characterization method can intuitively describe the creep variation. With the increase of the pre-deformation strain, the creep strain of the specimen firstly increases and then decreases. The increase of the pre-deformation strain can promote the course of aging precipitation, and improve the formed alloy’s tensile properties at room temperature, the Kahn tearing properties, and the fatigue propagation properties. Pre-rolled specimens produce a slightly weaker work hardening than pre-stretched specimens, but they also create a stronger aging-strengthening effect;thus the strength, toughness and damage performance can be improved to some extent. Among all the types of specimens, the specimen with 3% rolling after CAF treatment has the best comprehensive mechanical properties.
基金supported by the National Natural Science Foundation of China(Nos.51905424,51522509,and 51235010).
文摘Non-isothermal Creep Age Forming(CAF),including loading,heating,holding,cooling and springback stages,is an advanced forming technique for manufacturing high performance large integral panels at short production period and low cost.However,the creep deformation and aging precipitation during heating stage is often neglected in experiments and modeling,leading to low forming precision.To achieve shape forming and property tailoring simultaneously,a deep understanding of the non-isothermal creep aging behavior and the establishment of predictive models are urgently required.A new five-stage creep feature of Al-Cu-Li alloy during the non-isothermal creep aging is observed.The microstructural interactions between the dislocations,solute atoms,Guinier Preston zones(GP zones)and T1 precipitates are found to dominate the five-stage creep aging behavior.The physical-based model considering temperature evolution history is established to describe the five-stage creep feature.The springback and yield strength of non-isothermal creep age formed plates with different thicknesses are predicted and compared by non-isothermal CAF experiments and corresponding simulations.The CAF experiments show that the springback and yield strength of the non-isothermal creep age formed plate are 62.1%and 506 MPa,respectively.Simulation results are in good agreement with experimental results.The proposed model broadens the application of traditional CAF models that mainly focus on isothermal conditions.
基金Project(51175022)supported by the National Natural Science Foundation of ChinaProject(51318040315)supported by the National Defense Pre-research of China+1 种基金Project(09000114)supported by Initial Funding for the Doctoral Program of BIGCProject(E-a-2014-13)supported by BIGC Key Project
文摘Hot stretch-creep forming （SCF） is a novel technique to produce hard-to-form thin-walled metal components. Comprehensively considering the analysis results of the springback angle, yield strength and microstructure, four hot SCF process parameters including temperature, stretch velocity, post stretch percentage and dwelling time of a Ti-6Al-4V alloy sheet were optimized using an orthogonal experiment. The results reveal that temperature is the most important factor on springback angle. The yield strength of the deformed material in 0° direction increases, while those in directions of 45° and 90° fluctuate around the original value. After hot SCF, the shape of some a phases changes from short thin grains to long slender ones, and the microhardness changes very little. The optimized parameters with temperature of 700 ℃, stretch velocity of 5 mm/min, post stretch percentage of 2% and dwelling time of 8 min are achieved finally.
基金Project(2021YFB3400903) supported by the National Key R&D Program of ChinaProject(1053320211480) supported by the Science and Technology Innovation Project of Graduate Students of Central South University,China。
文摘Creep ageing forming(CAF)has been widely used in the aerospace engineering,but how to optimize the processing conditions,especially under complex stress state of the CAF process for large-size components produced by friction-stir welding is still a great challenge to now.In this work,the creep ageing behaviors and underlying microstructure evolution of a thick friction-stir welded Al-Cu alloy plate after CAF process under different stress levels are systematically investigated.The creep strain and the strength of the joint are both significantly increased when the stress is close to the average yield strength of the initial weld joint.The grain size reduces while the local strain and dislocation density increase from top to bottom of the NZ;hence,the bottom layer of the weld joint exhibits higher creep strain and steady-stage creep strain rate during the CAF process.The results reveal that the gradient microstructures sensitive to the stress level effectively govern the creep-ageing performance from the upper to the bottom layer in a thick friction stir welded Al-Cu alloy plate.Rationally increasing the initial dislocation density of the weld joint can both enhance the tensile properties and promote the creep deformation of the weld joint for CAF process.
基金the National Key R&D Program of China(No.2017YFB0306300)the National Natural Science Foundation of China(Nos.51675538,51601060)+1 种基金the State Key Laboratory of High-performance Complex Manufacturing,China(No.ZZYJKT2018-18)the Fundamental Research Funds for the Central Universities of Central South University,China(No.2018zzts151).
文摘A unified constitutive model is presented to predict the recently observed“multi-stage”creep behavior of Al−Li−S4 alloy.The corresponding microstructural variables related to the yield strength and creep deformation of the alloy during the creep ageing process,including dislocations and multiple precipitates,have been characterized in detail by X-ray diffraction(XRD)and transmission electron microscopy(TEM).For the yield strength,the model considers the multiphase strengthening behavior of the alloy based on strengthening mechanisms,which includes shearable T1 precipitate strengthening,non-shearable T1 precipitate strengthening andθ′precipitate strengthening.Based on creep deformation mechanism,the“multi-stage”creep behavior of the alloy is predicted by introducing the effects of interacting microstructural variables,including the radius of multiple precipitates,dislocation density and solute concentration,into the creep stress−strain model.It is concluded that the results calculated by the model are in a good agreement with the experimental data,which validates the proposed model.
基金Project(2017YFB0306300)supported by the National Key R&D Program of ChinaProjects(51601060,51675538)supported by the National Natural Science Foundation of China。
文摘The effect of temperature in range of 155-175 ℃ on the creep behavior, microstructural evolution, and precipitation of an Al-Cu-Li alloy was experimentally investigated during creep ageing deformation under 180 MPa for 20 h. Increasing temperature resulted in a noteworthy change in creep ageing behaviour, including a variation in creep curves, an improvement in creep rate during early creep ageing, and an increased creep strain. Tensile tests indicate that the specimen aged at higher temperature reached peak strength within a shorter time. Transmission electron microscopy(TEM) was employed to explore the effect of temperature on the microstructural evolution of the AA2198 during creep ageing deformation. Many larger dislocations and even tangled dislocation structures were observed in the sample aged at higher temperature. The number of T1 precipitates increased at higher ageing temperature at the same ageing time. Based on the analysed results, a new mechanism, considering the combined effects of the formation of larger dislocation structures induced by higher temperature and diffusion of solute atoms towards these larger or tangled dislocations, was proposed to explain the effect of temperature on microstructural evolution and creep behaviour.
