In order to produce a high strength brazed joint of A5056 aluminum alloy containing magnesium of about 5 mass %, the authors applied the flux-free brazing method with the aid of ultrasonic vibration to the aluminum alloy by selecting pure Ag foil as brazing filler metal and examined the effect of brazing conditions on the joint properties. The main results obtained in this study are as follows.
At the brazing temperature of 570°C just above the eutectic point of Al-Ag binary system, applying of ultrasonic vibration for 4.0s provided the brazed joint with the maximum tensile strength and the strength decreased with the applying time. When the brazing temperature was varied from 550°C to 580°C and the applying time of ultrasonic vibration was kept constant at 4.0s, the joint brazed at 560°C attained the maximum tensile strength and fractured in the base metal. It was found that using a pure Ag foil as brazing filler metal successfully brazed A5056 aluminum alloy and the joint strength was equivalent to that of the base metal. Fracture of the joint was prone to occur along (Al₃Mg₂+Al-solid solution) phase with high hardness formed at the grain boundary of the base metal. The amount of the hard (Al₃Mg₂+Al-solid solution) phase increased with the ultrasonic applying time and the brazing temperature. It seemed that the increase of the hard (Al₃Mg₂+Al-solid solution) phase mainly caused the brazed joint strength to decrease.