Strength and Corrosion Resistance of Solder Joint in Ultrasonic Soldering of Aluminum using Quasi-Melting Solder

Abstract

In order to obtain high strength aluminum butt-joints with corrosion resistance, ultrasonic soldering of A1070 rods was conducted using quasi-melting Sn-xZn(x=23, 40, 82mass%) hypereutectic alloy. Ultrasonic vibrations were applied at soldering temperature ranging 220°C~300°C through A1070 rods without a solder bath. The tensile strength of the solder joints with Sn-23Zn or -40Zn alloy were higher than that of the joint soldered with Sn-9Zn eutectic alloy. The joints soldered with Sn-23Zn or -40Zn alloy showed the same strength as A1070 rods which employed the same heat treatment as the ultrasonic soldering process. The thickness of the hypereutectic solder layer in the joints was thicker than that on the Sn-9Zn solder layer because unmelted α-Zn solid solution should have prevented the solder from being pressed out of the joint gap by the applied pressure during soldering. Tensile tests of the joints after immersion in NaCl aqueous solution revealed that the corrosion resistance of the joints soldered with hypereutectic alloy was higher than that of the joint soldered with Sn-9Zn alloy. It is considered that the improvement was achieved by the thick hypereutectic solder layer which should have reduced the notch effect in the joints.