Microstructure And Property Of Nanoparticle-Induced Low Energy Ultrasonic Welding Of Cu-Al Joint

With the rapid development of the new energy vehicle industry,the requirements for the cruising range of new energy vehicles are getting higher and higher.The number of automobile battery modules is also increasing,and the rapid increase in the number of battery modules has gradually increased the requirements for battery packaging technology.Ultrasonic metal welding technology is often used in the packaging of battery modules.However,the output energy of the ultrasonic welding machine has an upper limit,resulting in a limited number of layers of metal foil that can be welded.Nowadays,most researches focus on the process parameters,and when the metal to be welded exceeds the energy limit of the welding equipment,the change of process parameters will no longer be beneficial for improvement.Therefore,through the exploration of the ultrasonic welding process and the ultrasonic welding mechanism,a feasible solution to reduce the welding energy is sought.In response to the needs of ultrasonic welding of Cu/Al dissimilar metals,different joint overlap types of Cu-Al and Al-Cu were designed,and the effect of ultrasonic input energy on the microstructure and performance of the joint was explored.The results show that: the thickness of the Al-Cu interface diffusion layer is greater,and the peak temperature of the Al-Cu is higher when the joint under the same welding energy.The integrity of the Al-Cu joint is worse than that of the Cu-Al joint when the welding is completed.Thus,the Cu-Al joint should be used in the welding process.Under the welding pressure of 45 bar,the amplitude of 55 ?m,and the welding energy of 400 J,the lap joint reaches the maximum tensile shear force of0.86 k N,and the joint fractures on the Al side.Based on the designed Cu-Al joint overlap type,the test of reducing the input energy of Cu/Al joint welding with nanoparticles was carried out.The results show that the strength of the joint with interlayer can reach the same strength level as the joint without interlayer at 400 J when the welding energy is 200 J.The reasons for reducing the welding input energy are that the joint with interlayer have more interface joining methods and the driving force for diffusion is more and the material flow at the interface is higher.Based on the assumption that the surface roughness of the material has an important influence on the welding process,the mechanism of ultrasonic welding and the reason why Cu nanoparticles reduce welding energy are further explored with the method combining of experiments and molecular dynamics simulation.The results of experiments and molecular dynamics show that the asperities on the Cu and Al interface contact connection,and then the micro-soldering joints continue to experience the process of tearing,fracture and connection at the beginning of the welding process.When the Cu and Al interface becomes relatively flat,the interface then realizes a wide range of connections.Therefore,the flow and filling effect of Cu nanoparticles reduces the welding energy loss from the bump contact to the smooth interface,so as to realize the Cu/Al joint interface metallurgy under low energy induced by the nanoparticles.