Understanding the formation mechanism of SiC/Al joints by U-TLP bonding with the inactive Zn interlayer

The ultrasonic-assisted transient liquid phase (U-TLP) bonding process is extremely fast, which is a great challenge to reveal the inherent mechanisms. Understanding the joint formation mechanism of U-TLP is essential for the joining process design. In this study, the SiC ceramics and 6063Al alloys were joined by U-TLP using a Zn interlayer. The process of removing the oxide film on the base metal involved cracking, flaking off, suspending, and fragmenting. The migration of the eutectic liquid phases frontier was very fast (within 1 s). The relationship between the thickness of the liquid layer and the ultrasonic action time was a power function. The typical microstructure of the SiC/6063Al joints was SiC/amorphous Al₂O₃/Zn-Al eutectic/ Zn-Al eutectoid/6063Al. The shear strength of SiC/6063Al joints increased with the interfacial bonding ratio and reached up to 27 MPa for the ultrasonic action time of 5 s. The metallurgical bonding at the SiC/bond metal interface was formed through the amorphous Al₂O₃ transition layer. The formation mechanism of the Al₂O₃ reaction layer was revealed based on the thermodynamics, kinetics, and acoustics cavitation theory. This will provide a guideline for the future U-TLP process design.