Hydro-forming Fracture Theory And Prediction Of AA2219 Friction Stir Welding Tailor Welded Blank

Recently,the traditional forming method of the ellipsoidal bottom of the rocket tank is to form the flap pieces and then weld them into a whole.Hydro-forming offers the possibility of forming the entire bottom.However,the entire forming has been limited by the tonnage of the forming equipment and the size of the aluminum alloy billet.Therefore,the friction welding tailor welded blank(TWB)is required in the forming process.The size of the weld zone of the FSW tailor welded blanks is very large,the mechanical property distribution of the welded joints is extremely nonuniform,and the deformation distribution during the forming process is also nonuniform and further cracking defects occur.To solve the above problems,this article proposed a GTN damage model based on TWB to predict the cracking process of TWB during hydro-forming,and at the same time guide the forming of the ellipsoidal scaled parts.In order to measure the local mechanical properties of FSW welded joints,the microstructure was used to determine the size of the micro-zones of the joints.The DIC test was used to measure the strain of the welded joints during uniaxial tension.The local mechanics of the micro-zones of the joints was obtained.The performance can be used as a numerical simulation of the material properties of the weld joint zone.The in-situ tensile test observed the evolution process of cracks in the weld and base metal specimen.Results showed that the crack initiation of 2219 aluminum alloy TWB was based on the nucleation and growth of micro-holes in the material.Thus GTN damage model can be used to predict the damage evolution process.The unknown parameters in the GTN damage model were obtained through the micro-holes identification of the SEM photo and the finite element inverse optimization designed by the orthogonal experimental design.The finite element simulation software ABAQUS 6.13 was used to numerically simulate the hydro-forming process of 2219 aluminum alloy TWB under different conditions.The simulation was performed to treat the welded joints as the two-zone structure of the weld and the base metal,and to give them the GTN damage model respectively.Results showed that the position of crack is different when the weld was at different positions of the sheet material;The solution treatment tended to make the deformation of the weld and the body performance uniform,but the limited height was reduced;The application of a stainless steel outer blank outside the TWB can increase the limited height while coordinating the deformation of weld and body.The 2219 TWB hydro-forming experiment was conducted.It was to verify the ability of the GTN damage model to predict the cracking from the fracture position,the limited height,the minimum thickness,the fracture pressure,and the maximum principal strain.The results showed that the experimental results were highly consistent with the prediction results.The GTN damage model can be used to predict the stamping and forming cracking of TWB.Using the GTN damage model of TWB to guide the forming of the ellipsoid reduction part,the numerical results showed that the hydro-forming and solid solution treatment can make the thickness of the weld and body uniform.The experiment was conducted to obtain a semi-ellipsoidal scale with a ratio of major and minor axes of 1.6.