Electric Current Effects On The Mass Transfer And Reaction At Sn/Cu And Sn-Bi/Cu Liquid Solid Interfaces

Recently,electric current as an auxiliary method of material processing and preparation technology has produced real success in the field of soldering,casting,powder sintering,etc.In spite of this,the mechanism was still explained unclearly under the action of current.Due to the formation of liquid-solid interface involved in all above processes with the fusion of low melting metal or alloy,the applied current may change the behaviors of dissolution,mass transfer and interface reaction,further to affect the processing and mechanical property of material.In view of this,the Cu/Sn(Sn57Bi)/Cu reaction couples were designed to study the liquid-solid interfacial behavior under current.And so as to reveal the processes of dissolution,diffusion and interface reaction better,the effects of the relevant factors such as temperature,current density,time,etc on interfacial microstructure were investigated.The main conclusions were as below.(1)Electromigration was observed at a low current density(110 A/cm~2).Cu atoms migrated from cathode to anode driven by the force of electric wind,and then precipitated out as IMCs.A more marked difference of IMCs layers at cathode and anode would appear with the increasing of time.The performance of Joule heat in substrate dissolution and interface reaction was exhibited by the rising temperature.(2)At the initial stage,When the interface reaction at cathode is significantly reduced or the interface product layer is close to the relative equilibrium state,the function of electromigration begins to become prominent.As the Cu atoms move from cathode to near-anode,a chemical potential gradient in the opposite direction of electromigration force will be formed,resulting the dissolution of the substrate and the growth of interface product reduced.(3)Sn/Cu system is susceptible to the effects of electromigration.In the process of electromigration,IMCs growth has a trend of firstly increases and then decreases and then increases,product layer at anode is thickened with the extension of time,and with the increase of current density,the way of IMCs growth at anode will shift from diffusion-controlled to reaction-controlled.However,In Sn57Bi/Cu system Cu atom diffusion flux caused by electromigration is small relatively,the thicknesses of interface product layers at both ends increase with the extension of time,and the differences of both ends are smaller.(4)The dissolution activation energy of Cu at cathode is Q=28.25 kJ/mol,less than Q=34.48 kJ/mol calculated under no current.this shows that the applied current can significantly reduce the dissolution activation energy of Cu at cathode,thus promotes the dissolution and diffusion of Cu atoms.At the same time,effective charge and electromigration force of Cu atoms in molten Sn at 510-660 K are calculated.The results are z*=0.51~1.53,and it decreases with the increase of temperature.