Service Performance Of AA5754 Aluminum Alloy Autobody Part Under Thermoforming Condition

In recent years,the increasing number of domestic automobiles poses challenges to energy and environmental protection.Automobile lightweight technology is an effective measure to achieve energy saving and emission reduction at the same time.Aluminum alloy has become an ideal lightweight material for automobiles because of its excellent comprehensive properties.However,the formability of aluminium alloy at room temperature is limited.Warm hot stamping technology is an effective way to improve the formability of complex body parts of aluminium alloy.The hot formability of aluminium alloy is affected by temperature and strain rate.The cost of experimental research is high and the process is tedious.The simulation method to accurately predict the failure of parts becomes the focus of research.Temperature has an effect on the volume fraction of damaged voids during warm forming.It is important to study the effect of forming damage on service performance of aluminium alloy under warm stamping condition for realizing lightweight design of body structure.Firstly,a simulation method of forming failure considering real-time temperature change was studied.Based on the self-defined thermo-constitutive model of 5754 aluminium alloy and the numerical prediction of forming limit curve,the three-dimensional forming limit surface(TFLD)considering temperature change is fitted numerically,and the LS-Dyna self-defined subroutine with TFLD is compiled,packaged into a solver for solving 5754 aluminium alloy forming simulation with temperature change,and the margin nephogram of the forming part at any time is obtained to judge the forming failure of the part.Afterwards,the influence of warm forming damage on service performance of5754 aluminum alloy was studied.Simulated experiments of pre-stretching to different degrees of room temperature and hot forming of aluminium alloys and service simulation test of forming specimens pulling and breaking at room temperature were carried out respectively.Stress-strain curves of materials stretched to different strain states under warm and room temperature forming conditions were obtained.The effects of thermal forming damage on yield strength,failure strain,tensile strength,strength-plastic product and residual strain ratio were studied.It is found that the comprehensive service performance of warm forming is better than that of room temperature and hot forming.Then,a constitutive model of material service considering warm forming damage is established to simulate more accurately.Finally,the warm forming and bending properies of the anti-collision beam was studied.Firstly,the simulation model of warm forming of side anti-collision beam was established,and TFLD was used to evaluate the forming quality.Then,the information of the simulation results,such as thickness and strain,is mapped to the bending simulation,and respectively,established the bending simulation models of anti-collision beam without considering the forming process,considering the effects of geometric deformation and forming damage.Finally,the errors of service performance such as bending stress,damage,bending load,plasticity and energy absorption without considering forming effect were analyzed.To sum up,this paper aims at realizing the lightweight of the body structure of aluminum alloy,and to study the warm forming technology of aluminum alloy,the failure judgement of warm forming and the crashworthiness of body parts and so on.