Microstructure and Mechanical Properties of AZ31B/LY12 Joints Using Zn/Ag–Cu–Zn/Zn Multi-Interlayers via Ultrasound-Assisted Transient Liquid Phase Bonding

The use of a Zn/Ag–Cu–Zn/Zn multi-interlayer was observed to avoid the formation of Mg–Al binary intermetallic compounds (IMCs), which cause embrittlement and low strength of bonding when dissimilar metals such as Mg/Al are joined using ultrasound-assisted transient liquid phase bonding (U-TLP). The change in the microstructure and mechanical properties of the AZ31B/LY12 joints at 410, 440, and 460 °C with prolonging ultrasonic treatment (UST) time was investigated. The results showed that the diffusion of Ag and Cu was faster into the brazing seam on the LY12 side than that on the AZ31B side with increasing UST and temperature. The IMCs on both sides of the joints were transformed with the diffusion of Ag and Cu. The transformation made the fracture path shift from the AZ31B side (410, 440 °C) to the LY12 side (460 °C), and the maximum shear strength of the joints from 43.3 (410 °C) to 65.7 (440 °C) to 84.7 MPa (460 °C). The IMCs on the surface of the fracture path corresponding to the joints with optimal mechanical properties changed from Mg7Zn3+MgZn2+α-Mg (410 °C) to MgZnCu+Mg7Zn3 (440 °C) to Al2Cu (460 °C)