Investigation On Interface Microstructure And Properties Of Cu/Al Bimetal Composite Conductive Joints

Cu/Al dissimilar bimetal composite structure using full performance and economic complementarity between copper and aluminum,gives play us the advantage of copper and aluminum,reducing the application cost,Cu/Al dissimilar bimetal composite structure is used such as power transformer,circuit breaker,electrical bus bar wire,etc.However,En the interfuce of Cu/Al dissimilar bimetal structure the hard-brittle and high electrical resistivity intermetallic compounds decreased the interface bonding strength,conductivity and corrosion resistance,shortened the service life of the Cu/Al dissimilar bimetal composite structure.In view of the Cu/Al conductive joints used as the cote component in zinc hydrometallrgy cathode electrode(ran actual application requirement,the properties and microstructure of Cu/Al joints made by Explosive welding and Casting was characterized,the influence law between micrastructure and properties was analyzed,the failure reasons of joints after service was obtained in this paper.And then,Cu/Al joints made transient liquid phase bonding was proposed to aim at the problems of Cu/Al interface and it’s microstructure and properties was studied.Finally,in the angle of microstructure,properties and thermodynamics Cu/Al joints made by three different methods whs analyzed and compared to get more proper method to prepare Cu/Al joints used for actual application,the following conclusions were obtained:1.Conductlve joint interface layer with about 350 μm in thickkness and three different intermetallic compounds made by Casting,existed defects such aas void,crack,unbonding,ect;Conductive joint interface layer with about 100 μm in thickkness and one intermetallic compound made by Explosive welding,existed one kind of intermetallic compounds,two kinds interface structures and crack;Microstructure,composition,cspecially defeets was the main factors effect the properties and service life of joints;Joints with no defects and thin interface layer is difficult to obtain by Casting or Explosive welding.2.Al-based interlayer was designed and prepared evidence for the principle of Transient liquid phase bonding and alloying,Cu/Al joints with good bonding and thin interface layer made by Transient liquid phase bonding with interlayer.The thickness of Cu/Al joints interface made by Transient liquid phase bonding increases quadratically when the annealing rises,showing that interface layer growth main issubjected to chemical reaction rate in interface.Crackle occurs in interface when the time of insulation and dwell over 10 min.The added interlayer solid-phase diffused firstly with base metal when Cu/Al joints made by Transient liquid phase bonding,The melting point of alloy composition lower than aluminum occured;There were liquid phaes between interlayer and base metal with futher diffusion,and then,isothermal solidification occured in interface leading to metallurgical bonding interface.3.Cu/Al conductive joints made by three methods of Casting,Explosive weding and Transient liquid phase bonding was analyze and contrast in the angle of the interface structure（microstructure,composition and species of phase）and properties（joint strength,electrical conductivity and corrosion resistance）.Results showed that Transient liquid phase bonding was with the min thickness,the lowest defects rate and the electrical conductivity and corrosion resistance of Cu/Al conductive joints made by Transient liquid phase bonding was better than the conductive joints made by the other methods,it’s joint strength was slightly lower than Explosive-welding’s.Transient liquid phase bonding was the better method to make Cu/Al joints in the angle of microstructure,composition,properties and thermodynamics.4.Al₂Cu phase in joints made by three different methods were analyzed by thermodynamic calculation and it’s absolute value was by low to high:Explosive-welding<Transient liquid phase bonding<Casting,showing the drive energy of Al₂Cu phase in joints interface made by Casting.