Study On Microstructure Evolution Mechanism Of Non-ferrous Metal Ultrasonic Energy Field Composite Welded Joint

Aluminum alloy has good ductility,thermal conductivity and electrical conductivity.At the same time,due to its low density,it is widely used in various lightweight designs.Similar to aluminum alloy,magnesium alloy has become an excellent lightweight structural material because of its low density,soft and easy processing and deformation.Copper has good thermal conductivity and conductivity,so it is widely used in electronic packaging,construction industry and various processing and manufacturing industries.Tungsten is a metal material with high melting point,high hardness and good thermal conductivity.Because of its high sputtering threshold,low tritium retention and good resistance to neutron irradiation,it is widely used in nuclear fusion reactor,kinetic energy armor piercing projectile and aerospace.In this paper,2024Al/Ag/2024Al,W/V/W,AZ31B/Ag/AZ31B and AZ31B/Al/Cu systems were made by ultrasonic composite solid phase diffusion welding,ultrasonic composite vacuum solid phase welding and ultrasonic induced transient liquid phase welding respectively.The effects of ultrasonic vibration in solid/liquid medium on the microstructure and properties of welded joints were studied.At the same time,the 2024Al/Ag/2024Al system is expected to replace the traditional Cu substrate electronic devices in extreme environments.In 2024Al/Ag/2024Al system,because the welding temperature is much lower than the Al Ag eutectic temperature,the whole process of the system is solid phase,so the sonoplasticity of ultrasonic vibration in solid medium is studied.With the increase of ultrasonic vibration time,the intermetallic compound Ag₂Al generated in the weld shows a square growth trend.A model is established to calculate the diffusion coefficient.At this time,the diffusion coefficient is much higher than that without ultrasonic vibration.It is found that the external ultrasonic action will increase the internal friction of the material,which is the process of increasing the activation energy under stress induction.The external load ultrasonic energy field has a certain impact on the original relatively stable state of the metal.According to HRTEM,dislocations and twins are observed in the joint,and dislocations and twins are concentrated on the side with lower stacking fault energy,which shows that the metal with lower stacking fault energy is more prone to plastic deformation under the action of ultrasonic vibration.At the same time,amorphous Ag₂O was observed between dense hexagonal intermetallic compound Ag₂Al,and body centered cubic intermetallic compound Ag₃Al,which confirmed that amorphous can help connect substances with different crystal structures to a certain extent.In the W/V/W system,the ultrasonic composite vacuum solid-state diffusion welding process was selected to study the effect of ultrasonic vibration on the sonoplasticity of solid-state welding process in solid-state medium.Four different models were established to analyze the effect of ultrasonic vibration on solid-state welding.Based on the dislocation theory,a model is established to explain that the introduction of ultrasound will increase the strain rate of materials,So that the material softens;According to migwell Lagos diffusion welding theoretical model,it is explained that the introduction of ultrasound can shorten the welding time;According to the initial plastic deformation mechanism in the Derby model in the cavity closure theory of solid-state welding,it is analyzed that the introduction of ultrasound can reduce the welding pressure;Based on the diffusion theory,the diffusion coefficient and strain rate are establishedIt shows that the introduction of ultrasound can promote the diffusion between elements.In AZ31B/Ag/AZ31B system,the welding temperature is higher than the eutectic point and lower than the melting point,so eutectic liquid phase is formed at the interface.Therefore,the acoustic plasticity of ultrasonic in solid medium,cavitation effect and acoustic flow stirring effect of ultrasonic in liquid are studied.Binary eutectic reaction occurs in the joint,formingαWeld structure composed of Mg solid solution,Ag Mg₃intermetallic compound and Ag mg eutectic structure.When the ultrasonic vibration is 7 s,the average shear strength of the joint reaches the maximum value of about 66.87 MPa.