Study On Static Mechanical Properties Of AA5754 Aluminum Alloy Body Part Considering Warm Forming History

Under the background of automobile lightweight,aluminum alloys are widely used in automobile field because of its low density,high specific strength and corrosion resistance.However,the formability of aluminum alloy sheet is poor at room temperature.Warm forming technology with small springback and high precision can improve the formability of metal materials,which can be used to produce complex body parts.Due to the rolling process and other reasons,the aluminum alloy sheet has anisotropy.the deformation path of anisotropic sheet in complex stress states is obviously different from that of isotropic material,which leads to unreliable failure limit predicted by isotropic constitutive model.Furthermore,the warm forming process results in the change of the geometric and mechanical response of the formed parts,which brings a new challenge for the accurate prediction of the service performance of the components.Therefore,experiments and modeling of warm deformation and warm forming limit of anisotropic aluminum alloy were conducted.The influence of warm forming on the service performance of aluminum alloy was systematically investigated through mult-path two-stage loading tests consisting of warm prestrain and room temperature service,and the historical factors of warm forming were introduced into the performance prediction of complex warm forming components through modeling.This research is of great significance to the application of warm forming technology and the performance design for warm forming components of AA5754 aluminum alloy.In this study,the anisotropic thermal deformation behavior and warm forming limit of AA5754 aluminum alloy under warm forming condition were investigated by uniaxial tensile test in warm temperature,anisotropic tensile test and warm forming limit test.The results show that the forming limit of AA5754 aluminum alloy sheet increases with the increase of temperature and the decrease of strain rate;AA5754 aluminum alloy sheet shows thickness anisotropy and in-plane isotropy,and its anisotropy is not affected by temperature and deformation process.Based on the damage and fracture mechanism of aluminum alloy during warm forming,a unified anisotropic multi-axial damage constitutive model was established.The model takes into account the anisotropy of the aluminum alloy,coupling the factors of strain,strain rate and forming temperature,which reflects the warm deformation and failure law of AA5754 aluminum alloy well.The material constants in the constitutive equations were determined by genetic algorithm.The established constitutive model is proved to be effective in predicting the anisotropic deformation flow and warm forming limit of AA5754 aluminum alloy through statistical analysis and finite element model,which is helpful to the application of warm forming in industry.The evolution of hardening and failure behavior of AA5754 aluminum alloy under reloading after warm pre-forming was studied by mult-path two-stage loading tests.It is found that warm deformation has a significant effect on the static mechanical properties of AA5754 aluminum alloy.The aging softening and Bauschinger effect occur after pre-deformation of the sheet.The yield stress increases with the increase of pre-strain,and the failure strain decreases linearly with the increase of pre-strain.With the increase of forming temperature,the yield strength of the sheet decreases,while the hardening index and failure strain increase.The static mechanical properties of AA5754 aluminum alloy are not sensitive to the forming strain rate and stress state during the second loading stage.A damage constitutive model considering warm forming history was established to describe the subsequent hardening behavior and failure behavior of AA5754 aluminum alloy after warm pre-deformation.This model can characterize the aging softening and Bauschinger effect of AA5754 aluminum alloy after pre-deformation at different temperatures,predict the failure fracture of AA5754 aluminum alloy under complex stress states,and describe the ductility damage caused by pre-forming history at different temperatures.The material constants of the equation were determined by genetic algorithm and experimental results.The finite element simulation results prove that the constitutive model can effectively describe r the influence of warm pre-forming on the hardening and failure behavior of AA5754 aluminum alloy,and accurately predict the deformation and failure of AA5754 aluminum alloy under complex stress states.Based on the anisotropic multi-axis damage constitutive model and the damage constitutive model considering the warm forming history,the simulation coupling forming and service was conducted.It is found that the forming factors affect the failure mode of hat beam in three-point bending condition.The thickness thinning leads to the early failure,and the prestrain leads to the ductile damage of the side wall of the hat beam,which leads to the early failure and the crack propagation along the axial direction of the punch.Although the ultimate bending load of the cap beam is increased by 59.5%,the failure displacement is reduced by62.5%,and the energy absorption of the cap beam before failure is reduced by 42.9%.This study provides theoretical guidance for the performance design and prediction of warm formed components.