Abstract:The microstructure and mechanical properties of Al/Cu ultrasonic welding joints were investigated. Results show that: (i) the joint strength increased when the welding time increased within a certain range, and a maximal resistant force of 163.04 N was obtained when the welding duration and welding static pressure were 200 ms and 7.2 MPa, respectively; (ii) with a further increase of welding time, the bonding interface was gradually occupied by a thick strip layer of brittle Al 2 Cu (θ 2 ) phase, thus decreasing the strength; (iii) the maximum temperature in the welding region was 360 • C during the welding process, and a recrystallization phenomenon was identified near the welding interface; (iv) the average nanohardness of Cu, the Cu-Al interfacial reaction layer and Al were 1.04 GPa, 1.34 GPa, and 0.53 GPa, respectively, which is consistent with the formation of the intermetallic compound identified by energy-dispersive X-ray spectroscopy (EDS) and XRD analysis.