Study On Ultrasonic Welding Of Copper/Titanium Dissimilar Metals

With the development of science and technology,the demand of composite components welded by dissimilar metals in modern industry is more and more urgent.Cu/Ti composite structures not only meet the requirements for thermal and electrical conductivity of metal,but also have excellent properties such as corrosion resistance and low temperature resistance.However,the thermo-physical and chemical metallurgical properties of these two metals are quite different,and the fusion welded joints are more likely to form complex brittle intermetallic compounds Ti_x Cu_y.Compared with other welding methods of dissimilar metals,ultrasonic welding has the advantages of high efficiency and environmental protection,little deformation of welding,and not easy to produce brittle intermetallic compounds.Therefore,Cu/Ti ultrasonic welding has unique advantages.The ultrasonic welding technology was used to realize the connection of 1 mm thick T2 pure copper and 1 mm thick Ti6Al4V titanium alloy dissimilar metals.Based on the thermo-mechanical coupling,a three-dimensional finite element analysis model was established to simulate the temperature field and stress field distribution characteristics of the Cu/Ti ultrasonic welding joint under different welding process parameters.The effects of different welding process parameters on the interface morphology,microstructure and mechanical properties of Cu/Ti ultrasonic welding joints were studied.Zinc foil interlayer was used to change the structure of the interface layer of Cu/Ti welding joint,increase the effective bonding area of the joint,improve the mechanical properties of the joint and reduce the welding energy.The results of the finite element analysis are as follows:The temperature and stress fields of the Cu/Ti ultrasonic welded joints were non-uniform,the interface temperature and stress under the indentation were the largest and gradually decreased to the surrounding.With the increase of welding energy,the temperature diffusion area of the Cu/Ti joint interface gradually become larger,and the heat generated by the plastic deformation of the interface was far lower than the frictional heat.As the welding static pressure increased,the maximum temperature of the interface first increased and then decreased.The maximum temperature of the interface increased as the welding amplitude increased.The distribution of stress field in Cu/Ti interface was basically consistent.With the increase of welding energy,welding amplitude or welding static pressure,the distribution level of interface stress increased as a whole.The interface of the joints under different welding energies was relatively straight,and there was no intermetallic compound layer.When the welding energy was low,void defects appeared at the interface.With the increase of welding energy,the interface was well formed and the whole welding interface was effectively connected.With the increase of welding energy,the tensile force of the joint gradually increased,reaching a peak of 2190N with the welding energy of 3000J.With the increase of welding amplitude,the defects at the interface of Cu/Ti joint decreased gradually,and the tensile shear force increased linearly.With the increase of welding static pressure,the tensile shear force of Cu/Ti welding joint increased first and then decreased.When the welding static pressure was 0.4MPa,the interface void defect disappeared and the joint tensile shear force reached the peak value.By adding zinc foil interlayer,the effective bonding area of the joint interface was increased,and the structure of the joint interface was changed.When the welding energy was low,the interface structure was composed of copper solid solution and titanium solid solution.With the increase of welding energy,the microstructure of joint interface was composed of CuZn compound layer,copper solid solution and titanium solid solution.When the welding energy increased to 2000 J,the interface structure of the joint was composed of CuZn,Zn₁₅Ti compound layer and copper solid solution layer.When the welding energy was 2000 J,the tensile shear force of the joint reached a peak value of 2923 N,which was 33.5%higher than the maximum tensile shear force of the joint without zinc interlayer.