Microstructure and strength of ultrasonic-assisted brazed joints of Si₃N₄/6061Al composites

The ultrasonic-assisted brazing of 30 vol.% Si₃N₄/6061Al composites in air using a filler metal comprising a Zn-Al alloy was investigated. Effects of the ultrasonic action duration and brazing temperature on the microstructure and mechanical properties of the brazed joints were focused on. The surface oxide layer between the composites and filler metals appeared to be broken and gradually removed by the ultrasonic action, and a composite bond with uniformly distribution of the reinforcements was formed eventually. As the ultrasonic action duration and brazing temperature increased, the proportion of Si₃N₄ particles and the atomic percentage of Al in the bond layer increased. Increasing the brazing temperature led to grain coarsening of the α-Al phase. The maximum shear bond strength of the joints was 183 MPa, and fracture occurred on the Al metal matrix composites side. The higher strength was attributed to the α-Al phase and Si₃N₄ particles being uniformly distributed in the bond layers.