Microstructure and joint properties of ultrasonically brazed Al alloy joints using a Zn–Al hypereutectic filler metal

The ultrasound-assisted brazing of 1060 Al alloy using a Zn–14Al hypereutectic filler metal was investigated at different temperatures. The effects of brazing temperature on the bonding ratio, shear strength and microstructure of the joints were studied. Cavities and discontinuous cracks were found in the joint ultrasonically brazed at 410 °C, and the joint showed a low bonding ratio and poor shear strength. Excellent bonding ratios and high shear strength were obtained in the joints ultrasonically brazed at 440 °C and 470 °C. The primary α-Al phase showed a refined spherical shape in the joint ultrasonically brazed at 440 °C, but showed a coarse dendritic structure in the joint ultrasonically brazed at 470 °C and that brazed at 440 °C without ultrasonic vibration. The refined spherical microstructure shown in the joint ultrasonically brazed at 440 °C was attributed to cavitation-aided grain refinement effects.

► 1060 Al was ultrasonically brazed with Zn–14Al hypereutectic filler alloy.
► Joints brazed at the liquid state of filler had excellent joint qualities.
► Joint brazed near the liquidus temperature of filler had refined microstructure.
► The refined microstructure was attributed to the cavitation-aided grain refinement.