Matrix-dissolution-dominated interfacial reaction in ultrasonic soldering of SiCp/Al composites using Sn–Ag–Cu–Ti filler metal

The lack of reliable low-temperature joining solutions has hindered the application of SiC particle-reinforced aluminum matrix composites (SiCp/Al MMCs) in advanced packaging, such as for thermoelectric systems. This study investigates a low-temperature joining approach using a Sn–Ag–Cu–Ti filler metal assisted by ultrasound. Microstructural and thermodynamic analyses reveal a novel matrix-dissolution-dominated interfacial mechanism, distinct from conventional active soldering. Contrary to expectations, Ti does not participate directly in the interfacial reactions; instead, it plays a critical role in facilitating solder adhesion to the base material and assisting in subsequent removal of surface oxides, thus enabling pronounced dissolution of the aluminum matrix under the assistance of ultrasound. The liberated Al and Mg atoms form nanoscale amorphous reaction layers (Al₂O₃ and MgAl₂O₄) at the SiC interface, while a separate Al₂O₃/Ag₂Al structure forms at the Al interface. Driven by this unique bonding mechanism, the joints achieve a remarkable shear strength of approximately 56 MPa, where failure propagates through the solder, demonstrating superior interfacial integrity. This work elucidates a novel interfacial reaction pathway and provides a viable strategy for the low-temperature integration of metal-ceramic composites in thermal management applications.