Ultrasonic vibration treatment (UVT) was applied to an Al/Mg bimetal fabricated by lost foam casting. The effects of continuous and intermittent UVT on the microstructures and mechanical properties of Al/Mg bimetal interfaces were investigated. The results reveal that the Al/Mg interface without UVT is composed of an Al-Mg intermetallic compound (IMC) area and a eutectic area, and a thin oxide film exists at the boundary between the two areas, which inhibits element diffusion. The net-shaped Mg 2 Si gathers in the IMC area. Both continuous and intermittent UVT could remove the oxide film at the Al/Mg interface by acoustic cavitation and acoustic streaming effects. The Mg 2 Si particles are refined and dispersed at the whole Al/Mg interface. In addition, part of the eutectic Al-Mg structure is transformed into Al-Mg IMCs due to the promotion of element diffusion by UVT, which increases the homogeneity of the interfacial microstructure and microhardness. The shear strength of the Al/Mg bimetal composite with continuous UVT reaches 53.9 MPa, which is an increase of 63.8% compared with that of the bimetal without UVT. The interface thickness of the Al/Mg bimetal composite with intermittent UVT is lower than that with continuous UVT. However, the existence of pore

defects and local gathered Mg 2 Si particles decreases the strength of the material, but the shear strength still reaches 49.5 MPa.