Technologies Of Composite Bonds Of Al₁₈B₄O_33w/Al Composites By Ultrasonic Brazing

Al₁₈B₄O₃₃/Al composites were ultrasonic brazed by filling a Zn-Al eutectic alloy in air. The composite bonds reinforced by whiskers were focused on in this paper. The microstructures of bonded joints were examined by optical microscopy and a scanning electron microscope (SEM) equipped with an energy dispersive X-ray spectrometer (EDS). The shear strength of bonds was evaluated using a tension testing machine.Results shows that the liquid filler alloy can get into the clearance between the couples at 400℃in air and the oxide films on the surface of the composites can be removed by the action of ultrasonic vibration, and then the filler alloy can be well connected with the base materials, and the few whiskers can enter the bond by the action of the ultrasonic vibration. The penetration zones formed by holding on the high temperatures after brazing by ultrasonic, and the thin layers of base materials close to the bond can turn to a solid-liquid state by the diffusion and dissolved zones formed. Ultrasonic vibration was applied for the second time after the dissolved zones formed, the dissolved zones were mixed with and stirred into the bond region and a new composite bond reinforced with whiskers formed. The bonds with different whiskers volume content were realized by applying different brazing technologies. The bond with a shear strength of 203MPa was reinforced by a mount of uniformly distributed whiskers while ultrasonic vibration was applied for the second time after the couples were hold on 500℃for 5min. If pressing the couples before applying the second time ultrasonic vibration to extrude the liquid alloy in the bond region, the whiskers volume fraction of the composite bond can reach up to 14%-16% and the shear strength can reach to 223MPa.