Abstract: In order to realize the low-temperature direct bonding of TC4/AZ31 in the atmospheric environment, the surface modification of TC4 was carried out by employing ultrasonic-assisted pre-plating, and then the ultrasonic-assisted brazing method was used to realize the bonding between the modified TC4 and AZ31, which solved the problem that Ti and Mg elements could not be directly bonded due to their insolubility and non-reaction. Firstly, ABAQUS was employed to simulate the dynamic galvanizing process at the TC4 surface under ultrasonic action. The optimal ultrasonic-assisted pre-plating parameters were obtained: With a amplitude transformer immersion of 50 mm, a hot-dip temperature of 500 ℃, and an amplitude of 10 μm, the maximum flow rate at the TC4 surface in the zinc bath was 0.23 m/s, and the maximum sound pressure on the surface was 28.5 MPa. Secondly, ultrasonic-assisted hot-dip galvanizing was performed on TC4 to form a uniform (TiZn₃, TiZn₃ + TiZn₁₆, and η-Zn) coating on its surface. Finally, ultrasonic-assisted brazing was used to bond TC4/AZ31, and the effects of brazing temperature and ultrasonic time on the microscopic morphology and properties of dissimilar joints were studied. The low-temperature bonding of galvanized TC4 and AZ31 was realized at 230 ℃. The brazing seam was composed of (TiZn₃, TiZn₃ + TiZn₁₆, and η-Zn) layer, (β-Sn + η-Zn) layer, and Mg₂Sn. With the increase of ultrasonic time, the thickness of Mg₂Sn increased, and the overall width of the brazing seam decreased. The shear strength of the joint was controlled by the thickness and morphology of the brittle Mg₂Sn layer. When the ultrasonic time was 5 s, the thickness of Mg₂Sn was 6.7 μm, and the shear strength of the Ti/Mg dissimilar joint reached 47.7 MPa.