Comprehend Pulsed Current Assisted Hot Forming-Die Quenching Process Of 5A90Al-Li Alloy Sheet

With the lightweight and performance requirements of spacecraft parts,high specific strength aluminum-lithium alloy materials have been greatly developed in the aerospace field.However,the high strength of aluminum-lithium alloy at room temperature greatly limits its application in the spacecraft parts.The formed part of the subject is a stringer part,which is an ultra-long structural part that combines the characteristics of bending and deep drawing deformation.The dimensional accuracy and mechanical properties of the part cannot be guaranteed at the same time in the traditional hot process.The pulse current heating forming-die quenching composite process combines the rapid current hot forming with the heat treatment process.The aluminum alloy has poor formability at room temperature and the heat distortion of the parts are effectively solved after the heat treatment,and the production efficiency is greatly improved,the production cycle is shortened,and the production cost is lowered.The high temperature mechanical properties of 5A90 Al-Li alloy sheet were firstly carried out in this project to determine the forming properties of Al-Li alloy at different temperatures and forming rates.The current crack arrest mechanism was then explored through finite element simulations and experiments.The main reason for the occurrence of holes at the crack tip is that the local high temperature region is generated by the flow of current at the crack tip,and the internal crack of the material is finally cracked.In order to obtain the desirable process parameters of 5A90 aluminum-lithium alloy current heating forming-die quenching,the U-shaped part forming experiment was carried out to investigate the influence current heating temperature,heating time and subsequent aging environment on the dimensional accuracy and mechanical properties.At 360 °C or above,the springback of the part basically disappears.When the current density reaches 12.76 A/mm2,the maximum temperature of the sheet is 460 °C,and the temperature difference between the top and bottom fillet positions of the U-shaped part is less than 10 °C.The parts have the desirable strengthening effect under the solution conditions of 460°C/20 min and the aging conditions of 160 °C/10 h.The Vickers hardness of the part fillet position reaches 159.34 HV,and the tensile strength of the flat position reaches 512 MPa.Compared with the traditional aluminum alloy hot forming process,the composite process has great advantages in production efficiency and manufacturing cost.Through the independent design air-operated flexible electrode to improve the process automation,combined with finite element simulation and scaled-down parts experiments to reasearch the unstable position.Most of the area of the scaled-down stringer part are in a simple bending deformation state,the thickness is evenly distributed.Due to the complex deformation state of the composite of bending and deep drawing,the sheet at the axial position belongs to a local large deformation,and a strong thinning occurs during the deformation process.When the stringer part is formed at 460 ° C,the difference of wall thickness can be reduced to 0.187 mm.