Research On Pulse Current-assisted Bending Forming Law Of Titanium And Titanium Alloy

Titanium alloys have a wide application prospect in aerospace and other high precision fields owing to low density,high specific strength and good corrosion resistance.Meanwhile,the combination of high yield strength and low elastic modulus will lead to large springback occur during the forming process of titanium alloy,which makes it difficult to meet the requirements of precise plastic forming.Consequently,the application of titanium alloy is limited seriously.The pulsed current can effectively reduce the flow stress of refractory materials such as titanium alloy,decrease the springback and improve their formability significantly.In this paper,the influence of different electrical pulse parameters on the forming performance of titanium alloy was expounded by studying the process of pulse electrically-assisted TC4 titanium alloy and TA1industrial pure titanium alloy.By analyzing the experimental results of electrically-assisted uniaxial tension of TC4 titanium alloy,that shows the pulse current can effectively reduce the deformation resistance and improve the plasticity.The influence of different electrical pulse parameters on the limit of sheet bending and the law of springback was studied in the electrically-assisted bending experiment of TC4titanium alloy,which revealed that the evolution law of microstructure and properties in the process of bending deformation under the action of pulse current by combining with the distribution of temperature field.The results show that the pulse current can significantly improve the bending forming limit of TC4 titanium alloy,When the effective current is 2.4A/mm~2,the sample can be fully molded with good surface quality.In addition,the pulse current can effectively reduce the bending angle of TC4 titanium alloy.In the process of electrically-assisted bending,the temperature in the middle of the sample is the highest,and the temperature of the sample decreases gradually from the middle to both sides.Electron back-scatter diffraction(EBSD)measurement results show that the pulsed current can promote the motion of dislocation isocellular substructure,the content of small angle grain boundary is lower in TC4 titanium alloy after electrically-assisted bending.By electrically-assisted V-bending experiment of TA1 commercial pure titanium,the effect of pulse current on the bending performance of TA1 plate under different loading methods was studied.The results show that the pulse current can effectively reduce springback in the bending process under synchronous loading of TA1 plate.When the effective current density is2.8A/mm~2 and the duty cycle is 30%,the thermal stability temperature of the sample can attain to 490°C.There is no twinning in the inner layer,middle layer and outer layer of the plate,the tension-compression asymmetry is the weakest and the neutral layer migration coefficient is the smallest,then the springback is completely eliminated.Under the condition of asynchronous loading,electric pulse annealing can also reduce the bending springback.However,the springback angle is not as significant as that of synchronous loading under the same electric pulse parameters.In addition,the springback angle is almost the same under different pre-deformation conditions,and the amount of pre-deformation is not sensitive to the decrease of springback.