Ultrasonic Cavitation Erosion And Acoustic Field Simulation Of Oxide Film On Pure Aluminum During Solder Spreading

Aluminum alloy has the characteristics of low density,high specific strength and corrosion resistance,which is widely used in aerospace,rail transit and other fields.The existence of aluminum alloy oxide film greatly reduces the thermal conductivity and conductivity of aluminum alloy.Ultrasonic can effectively improve the wettability of aluminum alloy and break the surface oxide film.Ultrasonic brazing is easy to break the film due to cavitation,which makes the solder and the base metal form a good weld.However,the current research is limited to the observation of cavitation bubbles,and the quantitative relationship between the cavitation and acoustic parameters is not obtained.Therefore,the cavitation erosion of the anodic odide film is investigated both by experimental and simulation.This research will lay foundation for the quantitative understanding of the mechanism of the removal of aluminum surface oxide film.In the spreading test of pure Sn on alumina,a series of specimens with different cavitation areas and degrees were obtained by changing the ultrasonic action time.It is found that after ultrasonic treatment,cavitation pits appear on the surface of the base metal in the middle area on both sides of the interface,which is semicircular.With the prolongation of ultrasonic time,the semi-circular cavitation pits in the cavitation erosion area are continuously distributed,and gradually change to irregular concave cavitation pits,and semi-circular cavitation pits appear in both sides and middle areas of the base metal.After that,there are continuous cavitation pits in the cavitation area.There are semi-circular cavitation pits in the non cavitation area,and in both cases,the cavitation pits are all over the surface of the base metal.In the spreading test of pure Sn on the surface of alumina,the number and size of cavitation pits were measured and counted under different test conditions.The results showed that the longer the ultrasonic time,the more the number and size of cavitation pits,the greater the ultrasonic amplitude,the larger the number and size of cavitation pits,and the thicker the oxide film,the smaller the number and size of cavitation pits.The model of ultrasonic assisted wetting test was established by COMSOL software.It is found that the surface displacement field of base metal is regular and periodic under the action of ultrasonic amplitude of 20 k Hz and 4 ? M.After the ultrasound was applied,it reached the maximum value in the third cycle and reached the stable value at the 60 th cycle.The displacement field and sound pressure field are symmetrically distributed along the center line of the base metal.On the same vertical line,the displacement field of the base metal is larger and the sound pressure field is smaller.It is found that the larger the ultrasonic amplitude is,the greater the extreme value of displacement field and sound pressure field is.By comparing the results of the simulation and testing,it is found that the cavitation pits firstly appear at the interface of the base metal and the solder alloy at the side of the spread area rather than the center.It is assumed that before ultrasonic treatment,minor gas film exists between the oxide films of the solder and the base metal.The cavitation doesn't apply to the oxide film with the existence of the gas film.With ultrasonic action,the displacement amplitude of the base metal at the side is higher than the center,and the gas film is first disrupted.With longer ultrasonic treatment,the gas film at the center of the spread area gradually disappears.In this case the cavitation time beside the center last longer than at the center of the spread area,and thus the cavitation erosion of the side region is more severe.