Study On Unified Viscoplastic Constitutive Model And Hot Gas Forming For TA15 Titanium Alloy Tailor Welded Blanks

Titanium alloy has high specific strength,good high temperature performance,corrosion resistance.And tailor welded components has low manufacturing cost and short cycle.Titanium alloy tailor welded blanks have been widely used in the field of aerospace due to the combination of the above advantages.However,due to the existence of weld in tailor welded blanks,the deformation is non-uniform.How to improve the uniformity of material deformation is the focus of scholars.Finite element simulation is an important means of its research,and the constitutive model used in the simulation greatly affects the accuracy of the simulation results.The goal of this project is: Based on the unified viscoplastic constitutive model of tailor welded blanks established in this paper,a finite element model which can accurately predict the microstructure and deformation of tailor welded blanks in the forming process is established,and the means to improve the deformation uniformity of tailor welded blanks are proposed through hot gas forming experiments.In this paper,taking 3.5mm thick TA15 tailor welded blanks as the research object,the uniaxial tensile tests were carried out on the base metal and weld of tailor welded blanks in the temperature range of 850? ? 950?,and the microstructure after deformation was characterized by SEM and EBSD.The change rule of the material phase proportion,dislocation density,recrystallization and grain size were obtained.A unified viscoplastic constitutive model of tailor welded blanks is established.Based on genetic algorithm,a python program is written to fit the model coefficients,and a new objective function is proposed to evaluate the variation trend of variables.The fitting equation is in good agreement with the original data..The uniaxial tensile test with variable strain rate is designed,and the experimental results are compared with the prediction results of the constitutive model,which proves that the constitutive model established in this paper can accurately predict the flow stress of materials in complex deformation process.The hot gas forming experiments of cup-shaped parts were carried out with different forming pressures,and the geometry,wall thickness distribution and surface morphology of cup-shaped parts were obtained.It is found that increasing the forming pressure to a certain critical value can improve the wall thickness uniformity at the top of the middle section.Solution treatment can also improve the uniformity of the top wall thickness of the cup-shaped parts,but it will cause further thinning of the whole top material.The VUMAT subroutine of tailor welded blanks was written,and the finite element model coupling microstructure and deformation was established.The distribution and evolution of stress,strain and micro variables in the forming process of cup-shaped parts were obtained.By comparing with the experimental results,it is proved that the prediction results of the finite element model established in this paper are accurate.Compared with the finite element simulation using phenomenological constitutive model,the maximum relative error of wall thickness distribution is reduced from 26.3% to 9.18%.