Effect of rare-earth Sc on the interface microstructure and mechanical properties of Al/steel bimetallic composites prepared by liquid–solid casting

In this study, scanning electron microscopy (SEM), electron backscatter diffraction analysis (EBSD), and electron probe microanalysis (EPMA) were used to investigate the impact of rare-earth Sc on the interface microstructure and mechanical properties of Al/steel bimetallic composites fabricated by liquid–solid casting. With the addition of 0.3% Sc, the morphology of eutectic Si changed from needle-like to fibrous and granular. The addition of Sc did not change the types of intermetallic compounds in the Al/steel reaction layer, which comprised the Al5Fe2, τ1-Al2Fe3Si3, Al13Fe4, τ5-Al7Fe2Si, and τ6-Al9Fe2Si2 phases. The thickness of the first layer decreased, whereas that of the second layer increased as the Sc content increased to 0.3%. Furthermore, the Al5Fe2 and τ1 phase percentages of the reaction layer decreased, whereas the Al13Fe4, τ5, and τ6 phase percentages increased. Sc was mainly enriched in the front of the ternary compound layer (τ6) near the Al side. The addition of 0.3% Sc reduced the grain size of each phase in the interfacial reaction layer and did not change the preferred orientation of the Al5Fe2, Al13Fe4, τ5, and τ6 phases, but increased the polar density of the Al13Fe4, τ5, and τ6 phases and decreased the polar density of the Al5Fe2 phase. With the addition of 0.3% Sc, the average nanohardness of the reaction layer decreased by 5% and the bonding strength increased by 48%.