Research On Warm Forming Limit Of High Strength 7075 Aluminum Alloy Regarding Damage

With the increasing contradiction between energy supply and demand,it has become an urgent problem to be solved how to reduce energy consumption and reduce pollution.As one of the effective measures to realize energy conservation and emission reduction,more and more people have focused on lightweight technology.Aluminum alloy has been used in vehicle body as an ideal lightweight material,because of its excellent comprehensive properties.However,the formability of aluminum alloy at room temperature cannot meet the demand of production.Therefore,it has become a research hotspot that the combination of warm forming technology and aluminum alloy sheet to improve the formability and realize the production of complex parts.In the process of forming,people pay more attention to the position and state of material failure.Nowadays,although lots of scholars have done a series of research on the forming limit diagram of the metal material,there is little research on the forming limit diagram of the high strength 7075 aluminum alloy sheet under warm forming condition.In this paper,the warm forming limit of 7075-T6 aluminum alloy sheet is studied.Firstly,the thermodynamic properties of 7075-T6 aluminum alloy were studied based on the thermal tensile test platform,obtained materials tensile curves at different temperature(20?-500?)and different strain rates(0.1s-1,0.01 s-1,0.001 s-1),and the microstructure of specimens was observed and analyzed.On this basis,a unified viscoplastic constitutive model based on continuum damage is established.The results show that under the same strain rate,the strength of the material decreases with the increase of temperature,while the ductility decreases first and then increases with the increase of temperature;at the same temperature,the strength and strain rate increase with the increase of strain rate;the constitutive model can be used to describe the rheological behavior of 7075-T6 aluminum alloy at high temperature.Secondly,the warm forming limit test of 7075-T6 aluminum alloy sheet was carried out based on the forming limit test platform,and the forming limit diagram at 300? was obtained.Then,the forming limit prediction model of 7075-T6 aluminum alloy sheet was established based on the M-K theory and the continuum damage theory respectively.And the parameters of the models were analyzed.Investigation results show that the prediction results of the forming limit prediction model based on continuum damage theory are closer to the experimental results,and this model has wider applicability.Finally,the forming limit curves at different temperatures were predicted based on the forming limit prediction model,and the three-dimensional forming limit diagram(3D-TFLD)is established.In this paper,the research on the hot forming limit of 7075-T6 aluminum alloy sheet has provided some experience and guidance for the following research and application...