Microstructure And Formation Mechanism Of Interface Layer In Aluminum Alloy Resistance Brazing Joint Under Assistance Of Ultrasonic Vibration

In order to obtain a brazed joint with good comprehensive performance,using the effect of external physical field to obtain the required structure and performance,it is a hot topic of recent academic research.Traditional flux soldering is widely used in the field of aluminum alloy connection,which may induce the corrosion of the flux resistance and the formation of reaction bubbles,and thus deteriorates the strength and the corrosion resistance of the brazing joint.Basing on these questions,ultrasonic-assisted resistance brazing of 6063 aluminum alloy joints using Zn-2Al filler metals was performed in this study.The effects of sound field and electric field on the microstructure evolution of joints were significantly investigated.The effects of physical filed on the phase composition of Al/Zn-2Al/Al joints during brazing were analyzed.The dissolution process of the resistance brazed joint and the mechanism of ultrasonic refinement of the grain during the ultrasonic assisted resistance brazing process was obtained.Brazing joints were obtained with two-step direct current resistance brazing method using Zn-2Al filler metal.The electromigration behavior of Zn atoms in the joints interface were investigated by controlling the current flow direction.The effects of electromigration behavior on the microstructure evolution and the mechanism of electromigration behavior were analyzed.Results showed that,under the effects of electric field,the metal atoms diffusion were mostly driven by electric field and chemical potential,the chemical and electrical driving forces both influenced the growth of the solid solution layer at the joint interface.Al and Zn atoms migrated to the positive side at different velocities under the influence of the two driving forces.The back stress induced by the EM of Al promoted Zn migration to the negative side.The growth of the solid solution layer was promoted at the negative side and inhibited at the positive side during mass transport in the joint.We confirmed that the Zn atoms diffused along the grain boundaries under the combined effect of chemical and thermal gradients.The effects of sound field and electric field on the microstructure in the joints were investigated by observing the microstructure evolution in the interface of joints.Results showed that,sound field and electric field could change the microstructure of the joints and promote the dissolution of the aluminum base metal.The dissolution of Al elements in the base metal was intensified with the increment of ultrasonic power and current intensity under the assistance of ultrasonic vibration,and it results in changes to the microstructure of the interface of joints.Therefore,large amount of ?-Al phase formed in the bond with the application of ultrasonic vibration,Zn eleme nt was pushed out of intragranular.At the same time,the striated eutectic phases transformed completely into ?-Al eutectoid phases and ?-Zn phase,most of Al element and Zn element in the liquid phase were exhausted,which leads to the striated eutectic phase diminishing.Research shows that brazing joints were obtained with resistance brazing method,there are cracks and cavities in the interface of joints which would deteriorate mechanical performance of the joints.The application of ultrasonic vibrati on can remove existing oxide films and promote wetting of the solder on the substrate,and eliminate defects such as cavities and slag inclusion,while the application of ultrasonic vibration could also inhibit the element segregation in the boundaries.Based on the above research,the application 0f ultrasonic vibration could obtain a fine and uniform microstructure in the bond by promoting formation of eutectoid phase and decreasing eutectic phase during aluminum alloys resistance brazing.At the same time,it could obtain high-quantity joints through eliminate defects such as cracks and cavities,and inhibit the element segregation.These are the main reasons for the significant increase in the strength of the ultrasonic-assisted resistance brazing joints.