Study On Acoustic Cavity And Its Effect In Ultrasonic Soldering

Ultrasonic-assisted brazing is now more and more applied to the welding of difficult-to-wet materials such as ceramics,silicon carbide,composite materials,etc.The main reason for the wet connection of difficult-to-wet materials is the sound of liquid solder under ultrasonic action.The cavitation effect,the acoustic cavitation effect refers to the nucleation,growth,collapse of the cavitation bubble under the action of ultrasound and brings a series of physicochemical effects,which cause damage to the surface of the base metal.In this Paper,the morphological characteristics and time domain characteristics of cavitation bubbles generated by cavitation of free surface and narrow gap thin liquid metal are studied.The thin layer liquid pure tin solder for 1060 aluminum alloy base material under ultrasonic action is studied.The cavitation effect was finally calculated and analyzed by the finite element simulation software for the acoustic cavitation of thin-layer liquid metal and its effects.It is found that under the action of ultrasound,the cavitation bubbles at the bottom of the liquid metal are elliptical or nearly circular,ranging in size from a few micrometers to several hundred micrometers.The cavitation bubble volume in the free surface thin layer is larger than the cavitation bubble volume in the narrow gap thin layer.The bubble existence time is about 2-4 ultrasonic cycles,and the cavitation bubble in the thin layer of the free surface is longer than the cavitation bubble in the thin layer of the narrow gap.During the ultrasonic loading stage,there is a brief period of intense cavitation in the thin liquid metal.As the ultrasonic time prolongs,the periodic cavitation degree alternates.The cavitation intensity of the same component liquid metal in the same base metal fixture is affected by the ultrasonic power and the thickness of the liquid layer.The higher the ultrasonic power,the smaller the thickness of the liquid layer,the more severe the cavitation,and the greater the cavitation bubble density.The cavitation effect is caused by the high temperature and high pressure generated by the cavitation bubble collapse and the micro-jet flow destroying the surface of the base metal.The oxide film on the surface of the base metal can be removed and a cavitation pit can be formed on the base material matrix.Under the action of ultrasonic,the free surface thin layer of pure tin solder produces a cavitation pit diameter and depth ranging from tens to hundreds of micrometers at the bottom of the 1060 aluminum alloy solder pool.The bottom of the cavitation pit is covered with a few micrometers pits,and there are many intermittent microcracks at the bottom of the cavitation pit.The small crack is about a few microns long.The oxide film removal rate,cavitation pit density,and size are related to the degree of cavitation.When the ultrasonic power and solder composition are the same,the longer the ultrasonic action time and the smaller the liquid layer thickness,the more severe the cavitation degree.With the help of COMSOL Multiphysics finite element simulation software,the distribution and influence factors of the sound pressure value of the liquid metal at the bottom of the thin layer of liquid metal were simulated.The positive and negative sound pressures on the bottom surface of the liquid metal alternated in an ultrasonic cycle,and the maximum sound pressure reached 10~7Pa.Along the direction of ultrasonic propagation,the magnitude of the sound pressure in the solder pool changes,and the closer the distance from the ultrasonic head,the greater the sound pressure value.The simulation results of the influence factors of the sound pressure value show that the larger the ultrasonic power is,the smaller the liquid metal thickness is,and the greater the sound pressure value at the bottom of the solder pool.