Investigation Into The Electrically-assisted Roll Bending Process Of A TC4 Titanium Alloy Sheet

II Due to its higher strength and yield ratio and excellent corrosion resistance,titanium alloy have been widely used in aerospace field.However,the deformation resistance of titanium alloy is high,the plastic is poor and the springback is serious at room temperature,which brings a challenge to the precise roll bending process of cylinder or the variable curvature part of the titanium alloy.Based on the electroplastic effect of titanium alloy,this paper proposes a new process of electrically-assisted roll bending for titanium alloy plate.Meanwhile,the experimental study and theoretical analysis of roll bending process of TC4 plate under the different electrical parameters(including current density,frequency and time)was carried out.The specific tasks are as follows:(1)The mechanical properties under the electropulsing parameters of TC4 titanium alloys were studied by electrically-assisted uniaxial tensile experiments.The improvement of materials was compared with pretreatment and annealing treatment under the same conditions.Meantime,it is shown that the electroplastic effect can significantly reduce the deformation resistance of TC4 titanium alloy and improve its plasticity.In addition,based on microstructure analysis,it was found that electrical pulses could promote the occurrence of recrystallization of materials and improve the fracture form of materials.(2)To facilitate the study of springback mechanism of electropluse-assisted roll bending of TC4 titanium alloy plate,the experimental study,finite element analysis and microstructure analysis of the transient state of roll bending process was studied,namely,the forming of a circular arc of TC4 itanium alloy plate.Firstly,the instantaneous temperature field distribution in the process of electropluse-assisted bending was simulated through ABAQUS finite element analysis software to obtain reasonable electrical parameters.Then,combined with the bending experiment of the transient state of the electropluse-assisted bending experiment,the mechanism of the electropulse promoting to the springback suppression of the plate from the aspect of stress relaxation promoted by the electric pulse was explained.Meantime,the microstructure analysis shows that the electropulse can also promote the dynamic recrystallization of the material.(3)The experiment of electropulse-assisted continuous roll bending process was carried out.The temperature distribution of continuous bending forming assisted by electropluse was studied and the curvature radius stability of specimen of electropulse-assisted roll bending was analyzed.Meanwhile,based on the plane strain hypothesis and a flow stress model considerating electrical parameters,the relationship between springback and electrical parameters was derivated and the rationality of the model was verified by comparison into the experimental value.In addition,a new way of forming the curvature parts was obtained by applying the non-uniform electrical pulses into the material.Besides,through the analysis of microstructure,the effect of electric pulse on microstructure of deformation layer of titanium alloy was studied.