Effect of La on microstructure, mechanical properties and fracture behavior of Al/Mg bimetallic interface manufactured by compound casting

To improve the Al/Mg bimetallic interface, La was added into the Al/Mg bimetallic interface manufactured by a compound casting process. The effect of La addition on the microstructure, mechanical properties and fracture behavior of the Al/Mg bimetallic interface and the formation mechanism of the interface were studied in detail. Al11La3, Al8Mn4La, Al20Ti2La, and other rare earth precipitates (RE precipitates) preferentially precipitated at the interface with La addition, while the number of the Al11La3 and Al8Mn4La located in eutectic structure area (E area) gradually increased and aggregated in the interface with the increase of the La content. Besides, the matrix structure in different areas of the Al/Mg interface changed in different degrees, and the eutectic structure and primary γ (Mg17Al12) dendrites in the E area were refined, but the intermetallic compounds area (IMC area) had no obvious change. With the addition of the La, the interface was strengthened under the comprehensive effect of refinement strengthening and precipitation strengthening from the E area. When the La content increased to 1.0%, the shear strength of the Al/Mg bimetal reached the maximum of 51.54 MPa, which was 30.95% higher than the group without La addition. However, with the further increase of the La content, the large area aggregation of the Al11La3 and Al8Mn4La occurred in the interface, leading to the separation of the matrix structure of the E area and the decrease of the shear strength of the Al/Mg interface.