Study On Hot Forming Properties Of 7A04 High Strength Aluminum Alloy Sheet

With the development of the concept of "light weight",the optimization of structural design and the use of lightweight materials have become the focus of extensive research.Lightweight materials include new lightweight materials and ultra-high strength steel.High strength aluminum alloy as a new type of lightweight materials has been developed into a wide range of new automotive materials.Therefore,the forming process of high strength aluminum alloy is an important developing direction in the field of material processing.Because of the poor formability of high strength aluminum alloy at room temperature,the hot forming process will be the main processing method.This paper selects 0.8mm thick 7A04 high strength aluminum alloy plate as the research object.Through the tensile test,Dynaform simulation analysis,drawing test and Erichsen test to explore the stamping formability of 7A04 high strength aluminum alloy sheet under different temperature.The high temperature tensile test of 7A04 high strength aluminum alloy sheet using WDW-100 E microcomputer control electronic universal testing machine.The mechanical properties of 7A04 high strength aluminum alloy sheet,such as elongation ratio,stress-strain curve,yield strength ratio and so on,under different temperature conditions were obtained by the experimental results.According to the true stress-strain curves,and converted to the effective stress-strain curves into the Dynaform software to simulate the drawing limit size of 7A04 high strength aluminum alloy sheet from room temperature to 450°C.The hot stamping test measured the limit drawing size by using HIF60 Komatsu servo press forming system,and calculated the values of LDR at different temperature.Cut the forming cup along the cylindrical longitudinal section to observe and measured the wall thickness,hardness and microstructure of different drawing region under the different temperature,and get the relationship between properties and microstructure.In addition,the expansion of the 7A04 high strength aluminum alloy sheet with temperature change was determined based on the stamping hot forming system,and the IE value of the cup at different temperatures was determined.Finally,the stamping process parameters of thermal forming were compared by orthogonal experimental method to obtain the optimal hot stamping process parameters combination of 7A04 high strength aluminum alloy sheet.The results show that the tensile strength of 7A04 high strength aluminum alloy sheet at room temperature is up to 560 MPa,but the extended rate is low,and the plasticity is poor.Sheet metal plastic will increase with the temperature rise,at 200 °C,the plastic rises is not obvious,and when the temperature rises to more than 300 °C,the plasticity of the material will be significantly improved.Through deep drawing and cupping test show that using hot stamping process can improve the stamping formability of 7A04 high strength aluminum alloy sheet,and the best forming temperature from 350 °C to 400°C.Using hot forming,the LDR value of the material is increased from 1.771 to 1.927,the drawing performance is improved by 8.8%.And the IE value of the material is increased from 3.826 to 4.261;the expansion of the material is improved by 11.37%.By orthogonal experiment,the optimal hot stamping process parameters combination of 7A04 high strength aluminum alloy sheet is 20% stamping speed,10 kN blank holder force,350°C heating temperature,and high temperature lubricating grease.Using the optimal stamping process parameters,compared to the stamping experiment at room temperature,the limit drawing size is up to 47.5mm,increased by 11.76%,and the IE value is up to 4.411,increased by 15.28%.Through the analysis of microstructure,it is concluded that the main reason for the increase of high strength aluminum alloy at high temperature is the dynamic response,which offset the work hardening caused by deformation.Due to the short heating time,the temperature of the sheet is rapidly cooled to room temperature and it still keeps the characteristics of high strength after hot drawing.