Studies On Spreading Of Active Filler Metal On Graphite Surface Under Ultrasonic And Its Impact Analysis

The liquid filler metal can spread on the surface of nonwetting solid under the effects of ultrasonic during the brazing operation.It exhibits the acoustic spreading characteristics,which makes it possible to braze poor wetting material by ultrasonic-assist without flux in air atmosphere.In this thesis,we studied the behavior of the active filler on the graphite surface under ultrasonic irradiation to improve the spreading properties of active brazing filler metal on the surface of graphite under the action of ultrasonic,the spreading mechanism and influencing factors of the filler metal during ultrasonic assisted active brazing process.In this thesis,we based on the solder spreading process under ultrasonic wave to capture the external characteristic by used high-speed camera.The solder tin activity graphite surface process is described in detail to analyzes the ultrasonic in the spreading process,effects factors of brazing under the effect of ultrasonic spreading by combing with ultrasonic wave propagates on the surface of graphite and properties of brazed joint interface morphology.The active filler metal can be spread out on the graphite surface by ultrasonic assisted process.Unlike the rigid substrate is ultrasonic attenuation quickly in the amplitude of the surface of graphite,which makes the action of ultrasonic acoustic wetting on the graphite surface is very difficult,however,the amplitude attenuation decreases and the sound spreading effect gradually strengthened along with the hole of the graphite surface is filled with solder.The liquid can the spreading on the surface of graphite filler while the ultrasonic power is large enough.The wetting spreading of the active brazing filler metal on the graphite surface is caused by the wetting reaction,active element Ti is key of the solder and the substrate reaction,and titanium solder is in high melting point compounds form.The thermal effect of ultrasonic can change the high melting point compounds size and shape,and to promote the decomposition of this compound,which facilitates the diffusion of Ti elements into the substrate and formed reaction layer,thus improving wetting spreading out of the brazing filler metal in the substrate surface.When an ultrasonic wave is applied to the active solder for a certain period of time,the interface of active filler in the solid particles and the solder matrix solder generates heat resistance,which resulting the energy concentrated in the boundary interface liquid solder with a high melting point phase,and promoted the high melting point Sn-Ti solid size became smaller.The high melting point compounds distribution.The oxide film on the surface of solder is the key factor to hinder the spread of solder,and the solder spread can be promoted and the brazing filler metal surface oxide film can be removed by applying ultrasonic waves,whereas the ultrasonic impact is limited.Fundamentally,improving the oxidation resistance of solder is improves the solder wettability and spreadability.The addition of aluminum to the active brazing filler metal Sn5Ag8 Ti promotes the selective oxidation of aluminum in the solder.Just in the oxidation occurs,titanium and aluminum in the solder competing with oxidation to produce the corresponding oxide,and after a period of time,the thin but dense film of Al2O3 can prevent further oxidation of titanium withstand the corrosion of other harmful elements in the air.The protective effect of ultrasonic drive active filler aluminum conditions significantly enhanced,and the protective effect of Al2O3 is mainly due to the effect of oxide film package solder surface,compact oxide film Al2O3,prevents the oxidation of titanium in unplugged part.Meanwhile,the thin oxide film is conducive to the ultrasonic to the film and to improve the wettability of solder.