Joined AZ31B Magnesium Alloys with Ag Interlayer by Ultrasonic-Induced Transient Liquid Phase Bonding in Air

AZ31B magnesium alloys are commonly used in lightweight structures of automobile and aerospace industry. In this work, the ultrasonic-induced transient liquid phase bonding technique is deployed to joint AZ31B magnesium alloys at 490 °C with Ag interlayer in the atmosphere. The effect of ultrasonic vibration on microstructure and mechanical properties of welding seam is investigated. As vibration duration increases, the width of the welding seam increases firstly and then decreases. When the ultrasound vibration sustained for one second, the eutectic reaction occurred in the contacting interface between Ag interlayer and the base metal AZ31B, resulting in formation of liquid phase and metallurgical bonding. When the ultrasound vibration sustained for seven second, the width of the welding seam increased to a maximum of about 303.1 μm and the average shear bond strength of the welding joint attained the peak value of about 66.87 MPa. When the ultrasound vibration sustained over seven seconds, the liquid phase is gradually squeezed out and the width of the welding seam decreases. α-Mg and AgMg₃ can be observed in the welding seam. The analysis shows that α-Mg has a certain strengthening effect. The whole process of appearance, growth and integration of α-Mg is analyzed.