| In recent years,in order to effectively reduce energy consumption and alleviate the severe situation of environmental pollution,lightweight has become the main development direction of the contemporary automobile industry.7075-T6 aluminum alloy has a low density,high strength,strong oxidation resistance and excellent physical properties,making it an ideal choice for materials required for components in the automotive industry.However,it is difficult to form 7075-T6 aluminum alloy sheet at room temperature,and the formability can be improved effectively by warm forming process.It is found that the overaging of T6 aluminum alloy will occur when the heating time is too long in the heating furnace,which will affect its performance.The heating history in the forming process is very important to the formability and mechanical properties after forming of heat-treatable aluminum alloy.Since the growth and coarsening of precipitated phase is a dynamic process,it takes a certain amount of time to complete,so improving the heating rate of aluminum alloy sheet and shortening the time of the sheet at high temperature may reduce the loss of material strength after forming.Based on this,contact heating warm forming technology(CHWF)is proposed in this paper.Aluminum alloy blank is heated by the hot blocks of high temperature,and then quickly transferred to the die to form.Due to the high heating rate of contact heating can make the blank quickly reach the forming temperature,the well-developed η’ can be retained and the small size of precipitated phase can be dissolved and re-precipitated under the action of stress field,reducing the degree of overaging alloy,which can ensure the mechanical properties of parts after forming.Although there have been a lot of researches on the warm forming process of high strength aluminum alloy sheet at home and abroad,few studies on the related experiments and microstructure evolution of CHWF technology be found.Therefore,in this paper,we carry out the contact heating experiment and optimized process parameters with7075-T6 aluminum alloy blank as the research object through the self-designed contact heating and warm forming experimental device,in order to find out the rules of the mechanical properties and formability of 7075-T6 aluminum under warm forming condition.The main contents are as follows:1.The mechanical properties and formability under the condition of contact heating and heating furnace were compared,and the grain changes and the evolution of precipitated phase under different heating histories were analyzed by DSC,EBSD and TEM.It was found that the quantity of enhanced precipitated phase inside the matrix under contact heating warm forming was more,and the distribution was more uniform to ensure the mechanical properties after forming.2.The formability of 7075-T6 at different temperatures was analyzed by contact heating warm tensiling test,warm drawing test,and the drawing forming simulation.The results showed that the formability of blank increased gradually with the increase of temperature.200℃could obtain better formability and ensured less loss of mechanical properties after forming.3.Combined with the response surface,the influences of temperature,pressure and pressure holding time on the mechanical properties of sheet metal during contact heating were studied.The parameters of contact heating process were optimized by genetic algorithm,and six Pareto optimal solutions were obtained.By using the process parameters in the Pareto set,the stamping test of U-shaped parts was carried out,and the change rule of hardness and springback angle of U-shaped parts were analyzed.After comparison,a group of process parameter combination suitable for the process production was obtained,that is,the temperature was 200℃,the pressure was 10 MPa and the pressure holding time was 16 s.Through this study,for the rapid and efficient heating of 7075-T6 aluminum alloy,improving its formability,alleviating the performance loss caused by over-aging,saving production time,reducing production cost,realizing the full utilization of excellent mechanical properties of aluminum alloy materials and developing scientific and reasonable forming process has a great significance for the wide application of high strength aluminum alloy. |
