Study On The Design Of Filler And Soldering Process Of AZ31 Magnesigum Alloy

The joining technology of magnesium alloys occupies an important position in the engineering application. As one of the three welding methods, magnesium soldering and brazing will play a huge advantage on the joining the magnesium alloys. But the previous research of the magnesium soldering can not meet the practical application in the engineering. Soldering magnesium with ultrasonic vibration is a kind of green and efficient methods, which remove the surface oxide film with its ultrasonic cavitations.In this paper, the properties of the three kind of solders, such as Sn-30Zn (wt%)、 48%Mg-43%Zn-9%Al (wt%) 及 47.4%Mg-52%Zn-0.6%Sn (wt%),were studied. At the same time, the soldering process was modified. During the research, microstructure observation, DSC, XRD, SEM and EDS were used. The major findings of the research are as follows:1、Sn-30Zn solder can wet the AZ31 base metal with the ultrasonic vibration in the air. At 350℃, AZ31 metals were joined with Sn-30Zn solder by ultrasonic soldering. According to the microstructure characteristics of the joints with different soldering parameters, the model of Sn-30Zn ultrasonic soldering process was set up. During the process, brittle Mg2Sn layer formed between the base metal and filler, which is the main cause of joints failure. Increasing the ultrasonic time and holding time of the joints increased the width of the Mg2Sn layer and decreased the shear strength.2、Two kind of magnesium based solders were designed and smelted, the chemical composition were 48%Mg-43%Zn-9%Al(wt%)and 47.4%Mg-52%Zn-0.6%Sn(wt%). The melting points of the two solders were 340.3℃ and 339.8℃, which were available for soldering magnesium at low temperature.3、Mg-Zn-Al solder were composed of Mg32 (Al,Zn)49 dendrite and a-Mg+MgZn eutectic phase. AZ31 alloys were joined with Mg-Zn-Al solder at 400℃, and the soldering beam mainly contained Mg32 (Al,Zn)49 and a-Mg+MgZn eutectic phase. Based on the characteristics of the joints, the effect of ultrasonic vibration on the diffusion of a-Mg was established. The joints with Mg-Zn-Al filler were brittle, and failed in the center of the joints during the shear experiments.4^ Mg-Zn-Sn solder were composed of massive MgZn and a-Mg+MgZn eutectic phase. comparison with the wetting properties of Mg-Zn-Sn with QJ201 flux, it is better to wet the base metal with the ultrasonic vibration, which decreased the depth of the corrosion of the solder. The soldering process of Mg-Zn-Sn solder was studied, and the joints with ultrasonic vibration for 10s, holding Omin at 400℃, and cooling by water got the best strength. When cooled in air, the grains of the joints are thick. On the other hand, the joins cooling by water got the thin a-Mg+Mg7Zn3eutectic phase, which increased the shear strength largely. For Mg-Zn-Sn joints, the Mg-Zn-Sn solder diffused along the grain boundary when holding time at the soldering temperature, which would worse the the mechmical properties of joints...