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[en] Highlights: • Fine-grained 7034 aluminum alloys were successfully joined with ZnAl alloys at only 420 °C assisted by ultrasound. • The Al content in bond layer increased with increasing of ultrasonic treatment time. • Cu can suppress the formation of brittle eutectic phase in the joint. • The tensile strength of joint reached 249 ± 12 MPa with Zn-5Al-3Cu solder. 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 °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%. The maximum tensile strength of the joints reached 208 ± 8 MPa and all fractures occurred in the brittle eutectic phase. For the Zn-5Al-3Cu solder, η-Zn and α-Al phases were identified in the bond layer. The maximum tensile strength of the joints was 249 ± 12 MPa, which was ~ 80% of the base metal after the same soldering thermal cycle. In this case, fracture occurred in the η-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 α-Al in the bond layer increased to 93%. The strength of the joints decreased as the brittle ZnAl eutectoid phase crystals appeared inside the α-Al phase in the bond layer.