Study On Microstructures Of Brazed Joints Composed By Sound Field And Electric Field

Electromagnetic force fluid driving effect,thermoelectric effect and the electromigration(electric transmission)effect induced by the electric field sense,as the "energy regulator" or "catalyst",played an important role in controlling of heat transfer,mass transfer and momentum transmission of metal in the material processing engineering.The cavitation effect,thermal effect and acoustic flow effect generated by the ultrasonic wave can accelerate the flow of medium and remove oxide film,and then improve the wettability.When ultrasonic is applied to the liquid solder,it will produce "acoustic cavitation" effect and "acoustic eddy current" effect.By using these characteristics of ultrasonic,the oxide film on the base metal and the solder surface can be broken,assist liquid metal to wett with the base material and speeds up the transfer rate of the interface substance.However,no combination of the acoustic field and the electric field in joining process has been done between.In order to explore the brazing mechanism of acoustic field combined with the electric field as the main research goal,the design and construction of composite welding device was completed by ourselves.In the air environment,the acoustic field and current were combined to braze 6063 aluminum alloys using Zn-Al alloy solder.During the heating process,the ultrasonic wave acts on the liquid solder.The amount of dissolved Al wire in liquid pure Zn was measured.It is found that ultrasonic cavitation can promote the dissolution of base metal.The forming process of brazed joints under different current loading modes was recorded by high-speed camera.The corresponding metallographic microstructures were compared and analyzed.It is concluded that the forming process of brazed joints is different under different current loading modes.It is found that when the current passes directly through the solder,the solder will melt almost at the same time.Due to the current beam effect,a part of brazing filler finally concentrates on the seam center.The grain size of the microstructure is the same in the brazing seam.When current flows through the center and sides,the brazing material is heated and melted indirectly by heat conduction.When current flows through the edge of the sample,the solder melts from both sides to the middle.Edge grain is coarse,and the intermediate grain is fine.When current flows through the center of the sample,the solder melts from side to side.The intermediate grain is coarse and the grain of the edge is fine.There are two steps in the field of composite brazing of sound field and electric field.The first step is to apply a small current to improve the contact condition between base metal and filler metal.The second step is to apply a large current to generate high resistance heat.The solder melts in a relatively short time,wet on the base metal and join with the base metal.The ultrasonic wave acts as a composite action on the second power.Using ultrasonic cavitation effect,the oxide film on the surface of Al base metal and solder can be broken.The wetting of the filler metal on the base material was promoted.When the propagation direction of the ultrasonic wave is parallel to the direction of current in the weldment,increasing the time of ultrasonic vibration can promote the dissolution of base metal to braze seam.The tensile strength of the brazed joint increases first and then decreases.Improving the amplitude of the ultrasonic wave can also achieve the same result.When the propagation direction of the ultrasonic wave is perpendicular to the direction of the current in the weldment,the ultrasonic vibration time is increased,and the wetting degree of brazing filler metal on the base metal is increased.Reduce the number of holes in the brazing seam.The tensile strength of brazed joints is increased.Improving the amplitude of the ultrasonic wave can also achieve the same result.But ultrasonic has little effect on the dissolution of base metal,and the tensile strength of brazed joints is not obvious.