Research On Deformation Behavior And Application Of Pre-deformed Aluminum Alloy Sheet With Different Strain Rate

Aluminum alloy is one of the most important materials for automotive lightweight applications.Aluminum alloy have poor plasticity and high springback at room temperature.However,high strain rate can significantly improve plastic deformation and reduce springback of aluminum alloy sheet.And aluminum alloy body may is subjected to different loads and different deformation conditions in complex application environments.Therefore,mechanical properties test,plastic deformation constitutive relationship,the fracture mechanism and microstructure changes were studied for car aluminum alloy sheet under different strain rate and different pre deformation.the formability experiment and numerical simulation are studied for aluminum alloy sheet under quasi-static and high strain rate.Forming process simulation and production of the actual car front cover plate were studied systematically.(1)The material stress-strain curve of different pre deformation under different strain rates for the aluminum alloy sheet were obtained by quasi-static tensile test and high strain rate dynamic tensile test.And mechanical behavior of different pre deformation under different strain rates for the aluminum alloy sheet were studied.Research shows that: compared with the quasi-static tensile,strength of aluminum alloy sheet had increased significantly under high strain rate.With the increase of pre deformation aluminum alloy sheet,the smaller the increase of tensile strength,the lower critical strain rate for increasing fracture strain.Fracture strain and adiabatic of aluminum alloy sheet gradually increases with strain rate under high strain rate.The plastic stress-strain-strain rate constitutive relation of 6014 aluminum alloy sheet was established based on tensile test data.Results of fitting curves shows agreement with the experiments.(2)Based on the tensile test of different conditions,fracture morphology and microstructure of aluminum alloy sheet were analyzed by the macro and micro analysis method.Fracture and deformation mechanism of 6014 aluminum alloy sheet were obtained for different pre deformation and different high strain rate.Research shows that the fracture form of 6014 aluminum alloy sheet is the ductile fracture with shallow dimples.The fracture form of different pre deformation aluminum alloy sheet is quasi-cleavage fracture with quasi-static condition.The dimples on the fracture surface of aluminum alloy plate become more and more deep with increase of strain rate at high strain rate,which is a typical ductile fracture.The original microstructure of aluminum alloy plate is equiaxed grain,and the grain size of aluminum alloy sheet is obviously elongated along the tensile direction.The grain size of high strain rate is obviously higher than that of the quasi-static sheet along the tensile direction.(3)Cone cup value and limit drawing value of 5182 and 6016 aluminum alloy sheet were obtained by experiment and simulation research.The effect of different hardening models on the simulation results of aluminum alloy sheet drawing were studied.Research shows that drawing of 5182 aluminum alloy sheet for 1.5mm thickness is better than that of 6016 aluminum alloy sheet.Composite properties of 5182 aluminum alloy sheet metal drawing for 0.85 mm thickness is better than that of 6016 aluminum alloy sheet.The depth and thickness distribution of the hollomom equation is close to the experimental results,and the forming load calculated by Power equation is close to the experimental value.(4)To obtain deformation regulations and results of electromagnetic forming process,the numerical simulations of aluminum alloy sheet electromagnetic property with high strain rate were studied based on the high strain rate plastic strain rate stress-strain relationship of 6014 aluminum alloy sheet and LS-DYNA3 D software.Results show that sheet of 1/2 coil radius near were the first got the electromagnetic force and rapidly increase to the maximum in electromagnetic bulging process of flat coil plate.the sheet have great momentum,and then electromagnetic force decreases gradually and the deformation velocity increases to the maximum value.Due to the inertia of the sheet material continues to deform and drive the surrounding area of the sheet deformation.(5)Based on the results of electromagnetic bulging and simulation results of aluminum alloy sheet with different voltages,the effect of different voltages on the electromagnetic deformation of aluminum alloy sheet was obtained.With the increase of voltage,bulging height and maximum strain of aluminum alloy sheet gradually increased,displacement,strain,velocity and strain rate of the same position of the sheet gradually increased.It shows a smaller error by compared between the simulation results and the experimental results of electromagnetic bulging.When the voltage is 4k V and 3k V,thickness of the maximum metal deformation area sheet is 0.71 mm and 0.775 mm,the simulation results are 0.696 mm and 0.789 mm.(6)Based on design and optimization of the die surface shape and the forming process parameters of the front cover of aluminum alloy,the effect of the die surface shape of the surface and the process parameters on drawing of the aluminum alloy outer panel is obtained.The forming quality of aluminum alloy covering part is greatly affected by draft angle,friction and blank holder force.Inspection of aluminum alloy front cover plate products were passed by optimizing the process parameters and the die surface shape.