Development of Al/Mg Bimetal Processed by Ultrasonic Vibration-Assisted Compound Casting: Effects of Ultrasonic Vibration Treatment Duration Time

In this work, ultrasonic vibration treatment (UVT) was introduced to improve the interfacial microstructure and bonding strength of A356/AZ91D bimetal processed via lost foam compound casting (LFCC). The interfacial microstructure and mechanical properties of the Al/Mg bimetal processed via LFCC with different UVT durations were investigated. Results revealed the UVT did not change the composition of phases at the interface. The Al/Mg bimetallic interface consisted of an intermetallic compound area (β-Al₃Mg₂ + γ-Al₁₂Mg₁₇ + Mg₂Si) and eutectic area (δ-Mg + γ-Al₁₂Mg₁₇ + Mg₂Si). When the duration of the UVT was increased, the gathered Mg₂Si particles at the intermetallic compound area were refined to sizes of no more than 5 μm and became more homogeneously dispersed in the intermetallic compound area and diffused in the eutectic area, which could be attributed to the removal of oxide film and the acoustic cavitation and streaming flow effects induced by the UVT. The microhardness of the Al/Mg bimetallic interface was not obviously changed by the increase in UVT duration. The shear strength of the Al/Mg bimetal was increased with UVT and reached maximum with a UVT duration of 5 s, with a value of 56.7 MPa, which was increased by 70.3%, compared with Al/Mg bimetal without UVT. This could be attributed to the removal of the oxide film at the Al/Mg bimetallic interface, which improved the metallurgical bonding of the Al/Mg interface. Additionally, the refined and homogeneously dispersed Mg₂Si particles played an important role in suppressing the propagation of cracks and enhancing the shear strength of the Al/Mg bimetal.