Study On Ultrasonic-assisted Resistance Brazing Of Aluminum Alloy

The resistance brazing which has the advantages of heat resistance,short heating time,small heat affected zone,small deformation and stress,is widely used in electronics,micro equipment and small medical equipment.Previous research shows that the application of the ultrasonic wave makes the resistance soldering joint bonding rate increased to 85%.Currently,resistance brazing is still limited to the welding of micro-materials,and there is no relevant research on the mechanism of ultrasonic resistance brazing.Therefore,the aim of this paper is to welded joint of larger size,and explored the mechanism of ultrasonic assisted resistance brazing,the ultrasonic resistance brazing device is designed and fabricated in this paper,and the ultrasonic resistance brazing of 6063 aluminum alloy in atmosphere was carried out by using Al-Si-Mg alloy as filler metal.The device is simple in structure,can provide instantaneous low voltage,high current,accurate welding pressure,and reduce ultrasonic attenuation,and the device is the first ultrasonic auxiliary resistance brazing device in China,and is authorized by the state patent.The two step resistance brazing process is studied and the optimum process is obtained in this paper.It is found that the burst phenomenon can form in the process of resistance brazing,while the ultrasonic vibration can eliminate the burst phenomenon.The direction and time of the ultrasonic and the geometry of the welding joint will affect the burst phenomenon.The two step resistance brazing method makes a larger area of metallurgical interface between the base metal and the filler metal,thus improving the connection condition between the filler metal and the base metal.It is found that the burst phenomenon is formed by the high current density in the molten filler metal under the influence of electricity,heat and force.When the ultrasonic vibration removes the oxide film in the contact area of the two parent material and the ultrasonic time is not less than 6 s,the burst phenomenon can be eliminated.By using the unequal size of the welded joint,the deviation of the filler metal in the joint is studied.At the same time,the high-speed diffusion of Si element and the formation and eliminate of crater crack are discussed under unequal and equal size conditions.It is found that,owe of the high current density and heat generation at the upper interface,and high heat dissipation at the lower interface,the deviation of the filler metal is produced.When the welding current act on the local region,the Si element in the molten filler metal is biased at the interface,and diffus es along the high diffusion rate channel(Al grain boundary)to the base metal.When the welded joints are unequal,the high-speed diffusion of Si is only produced in the region with high current density.The longest diffusion distance reached 958.3?m.Under high temperature conditions,the diffusion of Si makes that the base metal is excessively dissolved,and finally crater cracks is formed.Ultrasonic vibration can produce high temperature and the diffusion of Si elements in local area and solution p ore and crack crater crack etc.Based on the above analysis,the mechanism of resistance brazing and the change of current path of different joint geometry and with or without ultrasonic vibration are obtained.