Ultrasonic-assisted soldering of fine-grained 7034 aluminumalloys using ZnAl filler metals

Fine-grained aluminum alloys are very heat sensitive and overheating can reduce the strength of the material. Filler metals of Zn-5Al and Zn-5Al-3Cu alloys were used to join fine-grained 7034 aluminum alloy pieces by ultrasonic- assisted soldering at 420 degrees C. We observed excellent dissolution of the filler metal to the base metal. For the Zn-5Al solder, the Al content of the bond layer increased from 25 to 54 at.% when the ultrasound time increased from 5 to 60 s, resulting in a decrease of the volume fraction of the eutectic phase from 60% to 15%. Themaximumtensile strength of the joints reached 208 +/- 8MPa and all fractures occurred in the brittle eutectic phase. For the Zn-5Al-3Cu solder,eta-Zn and alpha-Al phases were identified in the bond layer. The maximum tensile strength of the joints was 249 +/- 12 MPa, which was similar to 80% of the base metal after the same soldering thermal cycle. In this case, fracture occurred in the eta-Zn phase. The higher strength is attributed to the absence of the eutectic phase. When the ultrasonic treatment time was increased to 60 s, the volume fraction of alpha-Al in the bond layer increased to 93%. The strength of the joints decreased as the brittle Zn-Al eutectoid phase crystals appeared inside the alpha-Al phase in the bond layer. (C) 2017 Published by Elsevier Ltd.