Study On The Mechanism Of Electroplastic Effect And Constitutive Relationship Of TC4 Titanium Alloy

As a lightweight structural material,TC4 titanium alloy is widely used in aeros-pace,automotive industry,medical and other fields because of its excellent properties such as low density,high specific strength and specific stiffness,strong corrosion resistance and biocompatibility.However,TC4 titanium alloy has poor plasticity at room temperature and is a typical difficult to form material,so it is limited in applica-tion.The electro plastic effect provides a new processing method for difficult to form materials.Therefore,the study of the electro plastic effect of TC4 titanium alloy is of great significance to the progress of TC4 titanium alloy processing technology.In this paper,the self-designed insulation fixture is used to carry out the electro-plastic unidirectional tensile test of TC4 titanium alloy with different electrical parameters.The constant temperature tensile test is carried out according to the different temperatures produced by different electrical parameters,and compared with the electro-plastic tensile test,so as to explore the influence of electrical parameters on the mechanical properties of materials in the electro-plastic effect.The electro-plastic constitutive equation of TC4 titanium alloy was established based on Johnson cook model.Finally,the microstructure analysis,fracture morphology analysis and transmission electron microscope analysis of the samples after tensile test are carried out to explain the micro mechanism of the electroplastic effect.The tensile test results under different conditions show that the tensile strength and plasticity of TC4 titanium alloy under pulse current are significantly lower than those at room temperature and without electricity.By comparing the real stress-strain curve with the same pulse current density and different duty cycle with the real stress-strain curve at high temperature without electricity,it is found that the duty cycle only affects the mechanical properties by changing the material temperature,which has nothing to do with pure electro plasticity.By comparing the real stress-strain curve with the same duty cycle and different pulse current density with the real stress-strain curve at high temperature without electricity,the results show that compared with the softening effect of temperature on the material,the pulse current density itself has always played a dominant role in the pure electro-plastic effect of the material.Based on the high temperature constitutive equation and adding electrical parame-ters,the calculated results of the constitutive equation of electro-plastic effect are basically consistent with the experimental results,which shows that the established constitutive relationship can well predict the change trend of flow stress of TC4 titanium alloy under pulse current.Combined with the macroscopic plasticity of TC4 titanium alloy,the microstruc-ture of the material was observed.It was found that the electroplastic effect can greatly reduce the macroscopic plasticity of TC4 titanium alloy β The phase transition temperature promotes the dynamic recovery and recrystallization of the material,produces "electronic wind force",makes the dislocations arranged in parallel,reduces the resistance of dislocation movement,and improves the plasticity.