Study On Microstructures And Mechanical Properties Of Aluminum Alloy Joints Obtained With Ultrasonic-assisted Brazing Method

Al alloys are extensively used in industries because of their excellent physicalproperties. Brazing is a common method for the joining of Al alloys. However,fluxes are always employed in conventional brazing method, which may induce theformation of reaction bubbles and slag in the brazing seam, and thus deteriorate thestrength and the corrosion resistance of the joint. In recent years, ultrasonic-assistedbrazing, which is known as a fluxless brazing method, has been widely studied inthe brazing of Al alloys and their composites. The interfacial wetting behaviors ofthe Al alloy joint during the ultrasonic-assisted brazing are largely investigated inprevious studies. However, little previous literatures have been found on themicrostructure optimizing of the Al alloy brazing joint under the assistance ofultrasonic wave. In this study, three main issues have been investigated. Firstly, theultrasonic induced interfacial wetting behaviors and the tensile failure modes for Alalloy brazing joint were investigated in terms of joint configuration. Secondly, themicrostructure evolution of the Al brazing joint under the effect of ultrasonic wavewas experimentally investigated, the relevant mechanisms were discussed. Thirdly,ultrasonic-assisted brazing of Al alloys using low melting filler metal was studied.The results obtained in this study are as follows.6061-Al butt joints were obtained with an ultrasonic-assisted brazing methodusing Zn-3Al filler metal. The optimized processing parameter obtained in this studywere that pressure1.6kg, ultrasonic vibration time6s, ultrasonic power267W,brazing temperature410oC. The highest tensile strength of the joints was156MPa. Achange for the optimized processing parameter could deteriorate the tensile strengthof the joint. SEM results of the joints showed that the widths of the brazing seamswere uneven, and the joints were composed of coarsened α-Al dendrites and Zn-Almatrix. The interfacial wetting behavior for the ultrasonically brazed Al butt jointwas base on the mechanical mechanism.1060-Al lap joints were obtained with an ultrasonic-assisted brazing methodusing Zn-3Al filler metal. Artificial spacers were used to confine the joint gap, sothat the microstructures of the joint can be refined by ultrasonic wave. Theas-brazed joints exhibit uniformed joint gap widths and excellent bonding ratios andshear strength. The shearing failures of the joints are mostly happened in the basemetal. A refined microstructure was obtained in the joint treated by pulse ultrasonicvibration during solidifying. The interfacial wetting behaviors and themicrostructure evolution of the joints were both caused by the ultrasonic induced cavitation effects.Sn-xZn low melting filler metals were used to braze6061Al alloy under theassistance of ultrasonic vibration. The brazing processes were performed at thesemisolid state or the liquid state of the filler metal. The strength for the joint brazedat230oC using Sn-9Zn filler metal was69MPa. Increase the Zn content in fillermetal increases the optimized brazing temperature, and deteriorates the jointstrength because of the softening of Al base metal. Through using SiC particulatereinforced Sn-9Zn filler metal and brazing in the same processing parameter, furtherincreasing the strength of the joint.