Preparation And Performance Control Of Ultrasonic Welding Joint For Cu Foam/Solid Al Sheet

The unique porous structure of foam metal imparted a variety of advantageous properties,including energy absorption,effective electromagnetic shielding,and outstanding electrochemical behaviour.Foam metals were deemed crucial for finding widespread application in electronics,chemicals,machinery,and aerospace sectors.Therefore,there was an urgent need for the research and development of foam metal joining process.In this thesis,the ultrasonic welding technology with low heat input,easy control and high welding efficiency was used to prepare the joint of Cu foam/solid Al sheet,and to study its performance regulation and forming law.Through the structural design and frequency correction of the anvil base and welding head to achieve a good combination of their acoustic characteristics and mechanical characteristics,the construction of a high-power ultrasonic welding system suitable for the preparation of Cu foam/solid Al sheet joints was completed.The three-dimensional shape of the joint surface and its characteristic parameters,the maximum tensile strength and fracture mode of the joint,the microscopic shape of the joint interface and its characteristic parameters were defined and extracted as the joint quality evaluation indexes,and the joint quality was comprehensively evaluated and classified based on the degree of plastic deformation of the joint,the degree of damage to the three-dimensional Cu foam skeleton and the effective joint efficiency.By considering the interaction of orthogonal tests to obtain the three main welding parameters on Cu foam/solid Al sheet ultrasonic welding joint shear tensile strength of the main order of influence,welding pressure and welding energy for the main impact parameters,the interaction between the three factors was not significant.The optimal combination of parameters obtained was welding pressure 0.5 MPa,welding amplitude 65 % and welding energy 130 J.The joint quality and connection efficiency were ensured,and the three-dimensional skeleton structure of Cu foam was retained to the maximum extent.Based on the established evaluation system for ultrasonic welding porous joints of Cu foam/solid Al sheets,the quality of the prepared joints was evaluated as underweld,good weld and overweld.The exploration of three-dimensional macroscopic morphology and deformation characteristics,fracture mode and mechanism analysis,and microscopic evaluation of connection quality for joints of different quality levels showed that the relevant indicators in the evaluation system could adequately meet the characterization needs of Cu foam/solid Al sheet ultrasonic welding joints.With the increasing welding pressure,the shear tensile strength and effective joint efficiency of the joint showed a trend of first increase,then decrease and finally increase,the degree of Cu foam thinning,and densification was increasing.The increase in welding pressure within a certain range was conducive to the increase in the effective contact area at the joint interface,the length of the interface connection and the degree of interface material flow.However,excessive welding pressure would inhibit the frictional heat generation and plastic deformation at the connection interface,but not conducive to the improvement of the quality of the joint connection.With increasing welding energy,the shear tensile strength of the joint showed a trend of increasing and then decreasing,reaching an optimum at a welding energy of 130 J.The joint presented a mixed form of interfacial fracture and fracture along the thickness direction of the Cu foam.High welding energy would lead to serious deformation and a certain degree of damage to the Cu foam,it was very easy to become a crack budding place,the performance of the joint was greatly reduced.There was no stable intermetallic compound formation at the interface of Cu foam/solid Al sheet ultrasonic welding joint connection,shear tensile fracture plastic deformation and necking phenomenon,the connection mechanism was mainly plastic deformation and material flow resulting in mechanical locking and atomic diffusion of metallurgical bonding.