**Huan Li 1,2,\* and Biao Cao <sup>2</sup>**


Received: 9 July 2019; Accepted: 7 August 2019; Published: 8 August 2019

**Abstract:** The Cu/Al dissimilar joint, welded by high-power ultrasonic welding technology, is still facing challenges despite the significant research attention it has attracted. In this work, the microstructure and mechanical properties of resistance heat-assisted high-power ultrasonic welding of Cu/Al are investigated, in order to obtain high-quality joints. The intermetallic compound (IMC) at the interface of hybrid welding is primarily composed of Al2Cu, and the additional resistance of heat reduces the thickness of this brittle IMC layer. The average shear stress for the joint prepared by hybrid welding is ~97 MPa, which is higher compared to the joint strength without resistance heat (90 MPa). Moreover, the duration of the hybrid welding process is shorter. Finally, the fracture of the hybrid weld is found to be a brittle–ductile hybrid mode.

**Keywords:** resistance heat-assisted ultrasonic welding; mechanical properties; fracture morphology; intermetallic compounds; microstructure
