Study On Failure Criteria Of AA5754 Aluminum Alloy And Application Under Warm/Hot Stamping Conditions

In recent years, with the rapid development of economy in our country, the domestic car ownership increases quickly.In positive ways, this shows that our country’s urbanization level improves gradually.But with the sharp increase in automobile, energy saving and environmental protection have become huge challenges which the various countries and automobile industry face.Countries have put strict policies and regulations on automobile emissions, fuel consumption.It is pressing for automobile production enterprises and scientific research institutions exploring automotive technology continuously to reduce fuel consumption and emissions.The application of car body lightweight technology has become a feasible method to solve the problem of car of energy saving and environmental protection and has be generally recognized by each car companies.In recent years aluminum alloy has become an effective alternative materials of steel to realize car body components lightweight.Great attention has been put on the application of aluminum alloy in car body by automobile enterprises,domestic and foreign scholars.As an important method to improve the forming ability of aluminum alloy sheet in stamping car body structure or covering parts, warm/hot stamping technology gets the attention of scholars both home and abroad.CAE simulation analysis has become an indispensable tool in the research on the formability of aluminum alloy.Forming limit diagram(FLD) is commonly used in finite element software as a criterion to analyse the result of plate stamping.But it is only allow to import one forming limit curve.However the formability of aluminum alloy under the conditions of warm/hot forming is related with temperature and strain rate which is different from cold stamping forming conditions which formability can be expressed by one curve.In addition, it is difficulty and expensive to obtain the FLD of warm/hot forming by experiment method.Therefore, it has guiding significance and reference values to establish the failure criterion when aluminum alloy is stamping under warm/hot conditions,not only from the perspective of the simulation analysis but also from the perspective of optimization of process parameters and mold design in practical production.First of all,based on the study of 5754 aluminum alloy warm/hot stamping,the material constitutive equation of damage mechanics is established,then the FLD of 5754 aluminumalloy under different temperature and strain rate in warm/hot stamping conditions is obtained by the method of numerical calculation.The result is compared with the experimental data and the accuracy of the FLD is verified,which can provide a reference for the research of failure criterion.Then, the cup drawing test finite element model is established and the simulation results under different forming conditions are analyzed.Thereby the cracking failure criteria and wrinkle failure criterion of 5754 aluminum alloy under warm/hot stamping are both established.In the study of cracking failure criteria,the material damage value is set up as an evaluation standard in cracking failure of metal sheet forming.In the study of wrinkling failure criterion, the percentage of blank holder displacement account to the thickness of the sheet is set up as an evaluation standard in wrinkle failure of metal sheet forming.Finally, through the establishment of finite element model of the car fender under warm/stamping forming conditions,the cracking failure criterion and wrinkling failure criterion concluded in previous study are both applied to the analysis of the stamping forming quality,in which the validity of the established failure criterion is verified.In the analysis result it shows that the formability of 5754 aluminum alloy is improved under warm/stamping forming conditions and good quality car fender simulation results are obtained.By using the failure criterion concluded in the study,the results of fender stamping simulation are analyzed within a range of blank holder force and the minimum blank holder force under which wrinkle failure will not appear is obtained.