Warm Bending Formability And Process Parameters Research Of 7A09 Aluminum Alloy Stringer Reinforcement

With the demand of aerospace lightweight,it is more and more important to study new lightweight materials for thin-walled structures such as stringers in aerospace field.7A09 aluminum alloy has the advantages of low density,high strength and corrosion resistance,which is widely used in aerospace and automobile fields.However,there is little research on the formability of 7A09 aluminum alloy under warm and hot conditions.Therefore,this paper studies the mechanical properties and forming quality of 7A09 aluminum alloy by warm forming process.Taking the inner truss reinforcement of aerospace rocket fuel tank as the research object,the different process parameters of warm forming of 7A09 aluminum alloy stringer reinforcement are analyzed,and the influence of the bending process parameters on the thinning is mainly studied.Firstly,the mechanical properties and constitutive equation of 7A09 aluminum alloy under warm forming condition were studied.The effects of heating temperature and strain rate on the properties of 7A09 aluminum alloy were studied by uniaxial tensile test at room temperature and uniaxial tensile test at high temperature.The results show that the tensile strength decreases with the increase of deformation temperature,The elongation increases with the increase of temperature and decreases with the increase of strain rate.Based on the uniaxial tensile test of7A09 aluminum alloy,the mechanical properties of 7A09 aluminum alloy were determined,and the fields & Backofen constitutive equation between different deformation temperature,strain rate and flow stress was established.Secondly,the numerical simulation of 7A09 aluminum alloy stringer reinforcement is carried out.Aiming at the problem of stringer stiffener thinning,the bending deformation of7A09 aluminum alloy stringer stiffener was numerically simulated,and the influence of reduction,forming speed and heating temperature on forming quality was studied.The results show that the minimum wall thickness of the parts decreases with the increase of the down force.When the down force is 4mm,the design and processing requirements can be met;when the forming speed is 1000 mm/s?6000 mm/s the change of forming speed has little influence on the thinning and surface quality of the parts after forming.When the forming speed is 5000 mm/s,the surface quality of the stringer part is ideal;with the increase of forming temperature,the surface quality of the stringer part is better.When the forming temperature is 175?,the results show that the minimum thinning rate is only 3.8%.It can be seen that the quality of the parts isthe best when the reduction is 4mm,the forming speed is 5000mm/s and the heating temperature is 175?.Finally,based on the numerical simulation,the experimental verification is carried out.The parameters of reduction,forming speed and forming temperature in numerical simulation were selected to carry out stamping test.The predicted value was compared with the simulation value,and the actual thinning rate was 2.52%,which verified the reliability of the simulation.In order to further prove the accuracy of numerical simulation,GOM grid test,micro Vickers hardness test and metallographic test were designed.The results show that increasing the forming temperature can effectively reduce the deformation in the forming zone of the part.When the forming temperature is cooled to room temperature,the strength of the formed part can be restored to the original sheet strength level,The secondary precipitates begin to grow,which further proves that the mechanical properties of the material can be improved by increasing the forming temperature.Finally,all the tests verify the reliability of the finite element simulation results.According to the actual equipment and production conditions,the process parameters of warm forming of 7A09 aluminum alloy are determined as heating temperature 175?.