Study On Mechanical Behavior Of Al6016-T4 Sheet In Metal Forming Process And The Influence Of Pulse Current On It

Light weight of automobile is a hot spot in the automotive industry and related raw materials industries.Vehicle weight reduction can effectively reduce fuel consumption and reduce emissions.Combined with numerical simulation technology,accurate material constitutive model and fracture criterion for important automotive lightweight aluminum alloy sheets can be used to describe the mechanical behavior,predict the forming limit,optimize the process parameters and improve the forming quality.By studying the influence of pulse current on the mechanical behavior of aluminum alloy,it is helpful to promote the new aluminum alloy forming process and improve the processing performance of it.In this paper,the Al6016-T4 aluminum alloy sheet was selected as the research object,and the influence of anisotropy and stress state on its mechanical behavior was investigated.Firstly,six kinds of sample were designed for uniaxial tensile test,and mechanical properties were obtained by DIC method.The anisotropy of Al6016-T4 aluminum alloy sheet was studied by comparing basic mechanical properties of each dog bone specimen.The true strain distribution of the specimens with different stress states before fracture was analyzed and the true strain evolution of different positions on surface during deformation were compared.By comparing load-stroke curves and strain evolutions of three different notched specimens,the influence of notch radius on the fracture behavior was analyzed.The experimental data were used to calculate the parameters of Hill48,Drucker and Yld91 yield functions and Swift,Voce and Swift-Voce hardening models.Different yield functions and hardening models were implemented into the finite element software ABAQUS/Explicit through the material subroutine VUMAT.By comparing the strain evolution,the accuracy of different hardening models on the mechanical behavior of Al6016-T4 is studied.Then predicted r values,predicted yield stresses and yield surface of three kinds of yield functions were compared to investigate the accuracy of different yield function preliminarily.In order to further investigate the effect of different yield functions on the description of mechanical behavior,load-stroke curves of different samples under different orientations in experiment and simulation were analyzed.By comparing the strain distribution and strain evolution of different samples in experiment and finite element simulation,the accuracy of the finite element model was reconfirmed in the view of strain.The experimental-simulated hybrid method was used to calibrate parameters of Oh,Rice-Tracey and DF2012 and their corresponding fracture loci of Al6016-T4 were constructed successfully.Three ductile fracture criterion were respectively implemented into ABAQUS/Explicit by VUMAT to predict ductile fracture of samples under different stress states,and the fracture strain and fracture displacement were compared to investigate the effect of three ductile fracture criteria on the prediction accuracy of fracture behavior of Al6016-T4.In order to study the influence of pulse current on the mechanical behavior of Al6016-T4 sheet,this paper analyzes the three aspects of current density,pulse frequency and duty cycle.25 sets of three-factor and five-level orthogonal tests were carried out.By analyzing the orthogonal test results,the combined effects of duty ratio and current density,current density and pulse frequency,pulse frequency and duty ration were studied respectively.It is determined that the pulse current can reduce the tensile strength and elongation rate of Al6016-T4 which decreases with the increase of current density and duty ratio.The order of influence of three factors of pulse current on the mechanical behavior is current density>duty ratio>pulse frequency.In order to further explore the effect of pulse current on the mechanical behavior of Al6016-T4 sheet,control variate method was adopted to conduct another 8 sets of experiment,and the infrared imager was used for temperature monitoring.Firstly,the pulse frequency was set as a single variable and the results show that the temperature rise is very small,and the influence of the pulse frequency on mechanical behavior is not obvious.Then the current density was set as a single variable.The results show that the temperature rise has softened the Al6016-T4,which alleviates the strain hardening phenomenon and reduces the flow stress,tensile strength and elongation of the material.In addition,the temperature rise increases with the increase in current density,which results in more obvious the softening effect.The increase in current density accelerates the principal strain evolution,which in turn promotes fracture of the sample.