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.
Effect of Cu content in core and Zn in filler of the brazing sheet of 0.2mm thickness as those of 0.3mm and 0.5mm has been investigated. Corrosion form changed from pitting to general corrosion by adding more than 0.2%Cu to core in the sheets of 0.3mm and 0.5mm thickness, while pitting corrosion occurred in all the 0.2mm thickness sheets even containing Cu after 20 days SWAAT. On the other hand, residual life after corrosion was greatly improved by suppression of localized corrosion even in the sheets of 0.2mm thickness clad with filler containing more than 1%Zn, independently of Cu content in the core. The suppression of localized corrosion was caused both by higher potential difference between filler and core, and by gradual potential slope formed in the core due to Zn diffusion during brazing.