Low-temperature joining of Fe-based amorphous foil with aluminum by ultrasonic-assisted soldering with Sn-based fillers

Abstract Low temperature joining of amorphous alloys has big challenges to prevent them from crystallization. An ultrasonic-assisted soldering method was proposed to join the Fe-based amorphous alloys with the aluminum plates in air by using Sn-based solders. No obvious defects were observed and the joining ratio was more than 90%. At the interface of solder/aluminum, scallop α-Al solid solutions were formed and large fretting (pits) with a size of 50 μm on the aluminum plates was found due to ultrasonic vibrations. At the interface of solder/amorphous, Fe–Zn intermetallic compound (FeZn 13 ) was probably formed. Its formation activation energy was approximately 30.9 kJ/mol between the amorphous iron and the Sn–9Zn during the solid state diffusion, which was much lower compared with crystallized couples. The enhanced diffusion/reaction and the much low activation energy in this work are probably attributed to the amorphous state of the Fe-based foils. Adding nickel in the Sn–Zn solder can improve the hardness of the joints by formation of NiAl 3 intermetallic particles and depress the corrosion on the aluminum. Both the initially interfacial wetting and the microstructure refinement during solidification of the filler solder were improved by ultrasonic vibrations.