| 7XXX aluminum alloy is widely used in aircraft wall plate manufacturing because of its low density,high strength,excellent ductility and anti-fatigue performance,it is used in fuselage,truss,wing,etc.Creep aging forming is a new technology to enhance the shaping quality and service life of the integral panel in the aircraft industry.It can not only use the creep relaxation behavior of alloy under the combined action of stress field and temperature field to obtain the whole wall plate which satisfies the shape size requirement,but also the alloy have good mechanical properties and corrosion resistance by using artificial aging.7050 super high strength aluminum alloy is selected as the research object in this paper,the effects of creep aging forming process with constant load,cyclic load and compressive load on the microstructure and properties of the alloy are discussed by hardness test,tensile property test,intergranular corrosion test,exfoliation corrosion test and electrochemistry,metallographic analysis and transmission electron microanalysis,and the corresponding behavior prediction model is also given.The research results can provide theoretical and experimental guidance for the study of the aging forming technology of other aeronautical aluminum alloy materials.The results indicate that1)Under the constant load creep aging,the aging temperature is the main factor affecting the creep rate and corrosion resistance of the alloy,and effect of the stress is small.The steady creep rate of the alloy increases gradually with the increase of temperature and stress.The relationship between the steady creep rate of 7050 super high strength aluminum alloy and the creep stress and the creep temperature can be expressed as ?=e12.226?1.66exp(-120536/RT).2)After traditional aging treatment,the main reinforcement phase of 7050 alloy is a large number of dispersion distribution of the ?' phase,and they became smaller slightly after constant-load creep aging.The hardness of the alloy increases.The grain boundary precipitation phases became smaller slightly and their distribution is discontinuous,the corrosion rate of the electrochemical corrosion decreases,and the corrosion resistance of the alloy is improved.The sample creep treated by 120?/150 MPa after 24 h has the nice comprehensive properties.3)Cyclic hardening occurs during cyclic creep,and the strain of cyclic creep aging specimens are lower than that of the constant-load creep aging specimens under the same process parameters.As the temperature rises,the strain difference between the two increases,and the stress change has less effect on it.Cyclic creep aging specimens have better comprehensive performance than traditional artificial aging,and have higher hardness and corrosion resistance compared with the specimens creep aging at high temperature under constant load.The sample cyclic creep treated by 140?/200 MPa after 12 h has the nice comprehensive properties.4)The springback amount of 7050 alloy during compressive load creep aging process is affected by a variety of factors,among which,the aging temperature is the main factor,the second is the aging time and finally the pre-bending radius.Increasing the aging temperature and prolonging the aging time can effectively reduce the springback.The relationship among the springback amount of 7050 alloy and the creep aging temperature,aging time and pre-bending radius can be expressed as S(?,t,R)=3.227lnR-0.213?-0.332t+97.74.Bending creep aging forming can effectively refine the precipitaitions and correspondingly,improve the strength and hardness of the alloy.The size of the grain boundary precipitation phase significantly reduced and their distribution is discontinuous,the corrosion performance of the alloy is also improved The sample creep treated at 140? for 12 h with a pre-bending radius 500 mm has the nice comprehensive properties. |
PDF Full Text Request