Overwhelming reaction enhanced by ultrasonics during brazing of alumina to copper in air by Zn-14Al hypereutectic filler

The ultrasonic-assisted brazing of α-alumina to copper was achieved in air without flux using Zn-14wt%Al hypereutectic filler at 753 K within tens of seconds. The effects of ultrasonic time on the microstructures and mechanical properties of joints were investigated. In the joint interlayer, large amounts of intermetallic phases consisted of binary CuZn5 embedded by many ternary Al4.2Cu3.2Zn0.7 particles were formed. At the ceramic interface, newly formed crystalline Al2O3 aggregated. At the Cu interface, acoustic corrosion on the copper resulted in depriving the surface oxides and forming many pits on its surface, which provided saturated Cu in the melted filler alloys during the brazing. The ultrasonic vibrations had distinct effects on the metallurgical reactions of the joints, resulting in intermetallic-phase-filled composite joints with shear strength of 66 MPa. The overgrowth of intermetallic compounds, the newly formed crystalline alumina, and the acoustic pits was probably ascribed to the ultrasonic effects.