Study On Mechanical Properties And Microstructure Of 7075 Aluminum Alloy Tailor Welded Sheet During Creep Age Forming

With the rapid development of the aviation manufacturing industry,the structure of the aircraft body has gradually developed toward large-scale,integration and high-performance.The integral panel has become a major structural component of modern aircraft manufacturing and has been widely used due to its unique advantages.The development of creep age-forming technology provides an effective way for the integrated forming of integral components represented by integral panel.This thesis takes T6 state 7075 aluminium alloy tailor welded blank as the research object,exploring the influence of different age-forming process parameters on the forming properties and mechanical properties of the material.In this thesis,various microscopic analysis methods such as metallographic microscope,scanning electron microscope and transmission electron microscope are used to characterize the microstructure.Orthogonal experiment results show that the significant effects of the age-forming parameters on the springback of the components are the aging temperature,the aging time and the mold radius.In the age-forming process of 7075 aluminum alloy tailor welded blank,when the aging time is certain,the rebound rate of the material gradually decreases with the increase of temperature,and when the temperature reaches 180? the rebound reaches a minimum of 41.81%.Therefore,when the aging temperature is constant,the rebound of the material decreases rapidly with the increase of the age-forming time and then gradually stabilizes at a balance point.The metallographic microscope and transmission electron microscope show that when the aging time is constant,prolonging the time of age-forming is beneficial to the precipitation of the strengthening phase GP zone and transient phase of the formed part,and promotes the continuous distribution of the precipitated phase on the grain boundary to intermittent distribution.Thus the strength of the formed part is significantly improved by the combination of the grain boundary precipitation method and the strengthening phase.When the aging time exceeds 12 hours and enters the aging phase,the strengthening phase begins to decrease.At the same time,the precipitated phase which is intermittently precipitated on the grain boundary is converted into a network precipitate and the strength of the formed part begins to decline.The fixedaging time is constant,and the increase of aging temperature also promotes the precipitation of the strengthening phase GP zone and transient phase during the age-forming process,and the strength of the formed part increases during this process.After the aging temperature exceeds 180 ?,the GP zone and metastable phase gradually transform into equilibrium phase,and at this time,the grain in the heat-affected zone is coarsened under the influence of temperature,and the strength of the formed part decreases rapidly.The tensile test shows that the fracture of the formed part is located between the heat-affected zone and the TMAZ.In the experiment of age-forming,both aging temperature and aging time contribute to the increase in the number and depth of fractured dimples and promote the plasticity of the material.Among them,the effect of aging temperature on plasticity is slightly higher than the influence of forming time.