Effects Of Current Density And Grain Size On Electrochemical Plasticization Of Copper

Numerous studies have shown that specific electrochemical conditions can reduce the deformation resistance of metals and improve the formability,and this phenomenon is known as electrochemical plasticization（EP）.Electrochemical cold drawing（ECD）developed based on EP provides a feasible new processing technology of high-strength and high hardness materials.The existing researches have indicated that current density and the microstructures of metals have significant effect on EP,but the influencing essences of these two factors still need further clarification due to the nature of EP is not fully understood.Therefore,this work first took single crystal copper bars as the model material to study the effect of current density on EP.Then,polycrystalline copper bars were used to study the influence of grain size on EP.The results showed that under the different current densities(3.3 m A cm^-2,5.0 m A cm^-2,6.7 m A cm^-2,8.4 m A cm^-2,and 10.0 m A cm^-2),the drawing force of the single crystal copper bars were all lower than that of the traditional cold drawing（TCD,without electrochemical environment）,and the drawing force first decreased with the increase of current density,but then increased after the density exceeded 6.7 m A cm^-2.The surface hardness value of the drawn bars also showed a similar change with the drawing force.The decrease of drawing force and work hardening in ECD is due to the increase of crystal plane spacing caused by the increase of additional dislocation flux,which increases the activated slip system,promotes the multi-directional slip and decomposition reaction of dislocations,makes the formation of mostly short-range wavy dislocations and dislocation loops,prevents the formation of fiber texture,thereby reducing the work hardening of the material and increasing the plasticity.However,with the increase of current density,due to the continuous increase of corrosion rate,corrosion products are deposited on the surface of the bar and thickened,the selective corrosion rate is reduced,the number of slip systems is reduced,the formation of dislocations is slowed down,and EP is reduced.In order to achieve the maximum plasticizing effect,the rate of formation and dissolution of corrosion products must be in a certain equilibrium state.The drawing force and surface micro hardness of polycrystalline copper bars at different grain sizes（18μm、51μm、100μm、178μm、393μm）were smaller than those of TCD,and as grain size increasing,these characteristics also decreased.The weaving structure was less obvious,the distribution was more dispersed,and the dislocation density declined.As can be seen from the dislocation configuration,as the grain size of the polycrystalline copper bar increases,EP becomes more significant as a result of the decrease dislocation density and uniform dispersion of dislocation accumulating at grain boundaries.The reasons is that as grain size increases,grain boundary density decreases and the number of activated slip system increases,producing a suitable conditions for multidirectional dislocation movement and resulting decrease in dislocation density,plasticity increases and work hardening decreases.