Influence Of Low-Frequency Vibration On The Compression Behavior Of T2 Copper

With the increasing complexity of microforming parts,the novel hybrid forming technique,vibration-assisted forming,has attracted extensive attentions,since it can reduce the forming load and improve the forming performance of materials.In this study,the compressive deformation behavior and microstructure evolution of T2 copper under lowfrequency vibration were investigated.Firstly,the influences of frequency,amplitude and feeding rate of low-frequency vibration on the room-temperature compression behavior of T2 copper were experimentally investigated.The results revealed that the vibration amplitude plays the most significant role during compression of copper,and the forming load is effectively reduced with the increase of vibration amplitude.The finite element simulation software ABAQUS was applied to analyze the influences of friction factors under different loading conditions.It was implied that,under high amplitude conditions,the interface friction between specimen and mold is slightly decreased by the low-frequency vibration.According to the stress superposition theory,the vibration-assisted forming is a dynamic loading process,and the superposition of stress leads to the increase of internal stress which can be as high than two times of the initial stress.Therefore,the required forming load is reduced.Moreover,under conditions with larger amplitudes,the actual strain rate becomes greater,which enhances the superposition of stress and results in a larger reduction of forming load.To investigate the influence of low-frequency vibration on the microstructure evolution,the metallographic observation experiments of specimens compressed with and without vibration were conducted.It is indicated that,under the low-frequency vibration mode,the grain refinement is accumulated,and the dislocations are massively generated as indicated by TEM observation.In the meantime,the dislocation density is much higher,and its distribution becomes more uniform,as revealed by the dislocation etch-pit corrosion experiments.Based on the results of microstructure observations,the microstructure formation mechanism under low frequency vibration was proposed.Under the lowfrequency vibration mode,cyclic impact loading leads to the increase of dislocation density,and results in the formation of dislocation cells which gradually evolve into new grain boundaries,leading to grain refinement.In addition,low-frequency vibration-assisted compression experiments and metallographic observation experiments were carried out with different-sized specimens.The results revealed that,obvious size effect exists during low-frequency vibration deformation.That is,the smaller the specimen size,the greater the forming load is reduced and the smaller the grain size is.The increase of forming load reduction rate is mainly due to the enhancement of the stress wave superposition effect and the decrease of the “surface layer” flow stress.The decrease of grain size is attributed to the further improvement of dislocation density,which is caused by the increase of strain rate.