Research On High Temperature Gas Bulging Forming Of Special-Shaped Thin-Walled Components For Rail Train

With the development of rail transport worldwide,research into the light-weighting of rail trains is gaining importance.Aluminium alloys are widely used in the manufacture of rail trains due to their high specific strength,low mass and good corrosion resistance.Poor formability and high springback may occur when aluminium alloys formed at room temperature.High temperature gas bulging forming can improve the forming quality and accuracy of parts,which is one of the important forming methods for aluminium alloy components with complex contours.This paper investigated the high temperature deformation behavior of 5083 aluminium alloy and conducted numerical simulation and experimental research on the high temperature gas bulging forming of aluminium alloy in door curved beam.Combining response surface methodology to obtain optimal forming parameters for severe thinning,uneven thickness distribution and low forming efficiency.Finally,the feasibility of the high temperature gas bulging forming process for in door curved beam of rail trains was demonstrated through gas bulging tests.The research for this paper is as follows:（1）The deformation behavior of 5083 aluminium alloy at high temperature was studied.The mechanical properties at different temperatures（450℃,480℃,510℃）and strain rates(5×10^-4s^-1,1×10^-3s^-1,5×10^-3s^-1,7.5×10^-3s^-1,1×10^-2s^-1)were investigated through high temperature tensile experiments.The variation of flow stress and elongation of the material under different deformation conditions was determined.The constitutive model describing the high temperature deformation behavior of the 5083aluminium alloy was fitted based on the Arrhenius equation.By analyzing the microstructure of the fractured specimen,it was determined that the microscopic mechanism of the 5083 aluminium alloy during high temperature deformation was mainly grain boundary sliding controlled by intra-crystalline diffusion.The fracture mechanism of the specimen was mainly along-crystal fractures accompanied by a little through-crystal fractures,and the fracture form was a microporous polymerization type fracture.（2）By using finite element numerical simulation techniques,the forward and reverse gas bulging forming process of special-shaped thin-walled rail train in door curved beam has been optimized.To solve the problem of excessive thinning,a quadratic regression model of the pre-forming die depth,the area ratio,the friction coefficient and the minimum thickness of the curved beam was established.The best combination of parameters was obtained:the pre-forming die depth was 71.128mm,the area ratio was 0.396 and the friction coefficient was 0.1.To solve the problem of uneven thickness distribution at fillets in the bottom,the pre-forming area was optimally regulated based on finite element numerical simulations.It was determined that the center of the pre-forming die should be located 15mm offset from the center of the final forming die in each negative direction of the X and Z axes.To solve the problem of low forming efficiency under the premise of ensuring the quality of part,the relationship between the gas pressure curve during forming and the minimum thickness and forming time was analyzed.The maximum strain rate of the blank during the forming process should be kept below 1×10^-3s^-1 and the rated gas pressure should be set at 2.0MPa.After optimization,the thinning of the part was reduced from 52.28%to 39.24%and the forming time was approximately 18 minutes,meeting the quality requirements.（3）Based on the optimization results of the finite element numerical simulations,high temperature gas bulging forming tests of special-shaped thin-walled rail train in door curved beam were carried out.The quality inspection of the test part showed that the thickness and contour accuracy met the quality requirements,which verified the precision of the numerical simulation calculation.The microstructure distribution of the test part was investigated by EBSD and other characterization methods.In the flange zone,the deformation of the blank was small and the internal dynamic reversion was accompanied by a little dynamic recrystallization.In the sidewall,the deformation of the blank increased,more dynamically recrystallized grains appeared between the grains and the intermetallic compound Mg₂Si precipitated.The presence of dynamic recrystallization and the precipitation of intermetallic compounds resulted in a more homogeneous distribution of grains.As a result the stability of the blank was improved during deformation.