Study On Effect Of Pulse Current On Properties Of TC4 Titanium Alloy Sheet

TC4 titanium alloy has excellent comprehensive properties such as high specific strength,high temperature performance and good corrosion resistance,which has been widely applied in aerospace,automobile,ship building,electric,energy,biotechnology and other fields.However,the plasticity of TC4 titanium alloy is poor at room temperature,which can easily cause a series of forming defects such as cracking and springback under the action of forming force,which makes its application limited.The pulse current assisted forming process can effectively reduce the forming force and improve the processing performance and forming quality of TC4titanium alloy.In this paper,the effect of pulse current on the microstructure and properties of TC4 titanium alloy is systematically investigated.By modifying the classical Hall-Petch relationship,the Hall-Petch relation of TC4 titanium alloy under pulse current is established,and the critical current density,9.07A/mm~2,satisfying the inverse Hall-Petch relationship is obtained.A functional relationship between elastic modulus and pulse current density is established,and some model parameters are obtained.The elastic-plastic flow stress model of TC4 titanium alloy under pulse current is established.The data of mechanical properties before and after the pulse current treatment of TC4 titanium alloy with prefabricated defects are obtained by the uniaxial tension test.Before and after the treatment,microstructure analysis about internal micro defects of TC4 alloy is carried out.The results indicate void volume fraction decreases from 2.18%to 0.86%when pulse frequency increases from 0 to 140Hz.Meanwhile,yield strength and ultimate tensile strength rise from 928MPa to 990MPa and from 954MPa to 998 MPa,respectively.Moreover,the elongation increases by 58.82%.When pulse frequency increases from 140Hz to 160Hz,void volume fraction increases from 0.86%to 1.99%.At the same time,yield strength and ultimate tensile strength decrease from 990MPa to 978MPa and from998MPa to 990MPa,separately.Elongation decreases by 35.19%.Void volume fraction,dislocation density and solid solution effect jointly determine mechanical properties of TC4 alloys with prefabricated defects.By means of salt spray test and microscopic analysis,the effect of pulse current treatment with different parameters on the corrosion resistance of annealed TC4 titanium alloy is studied.The results indicate that pitting corrosion is the main form of corrosion in TC4 alloys.Besides,with the increase of pulse current frequency,voltage and time,the corrosion resistance of TC4 titanium alloy has tendency to get better before getting bad.The parameters to obtain optimal corrosion resistance are pulse 200Hz of frequency,50V of voltage,1min of processing time,and corrosion resistance grade of TC4 titanium alloy can rise to 9 under this processing condition.