Preparation of Al-Fe Bimetal Composites using Solid-Liquid Compound Casting: Effect of Coating on the Interfacial Microstructures and Mechanical Properties

The integration of aluminium and steel as a single component by solid-liquid compound casting offers a pathway for producing lightweight and reliable strength. In this study, Al6061‑T6 aluminium alloy (AA) was cast onto mild steel (MS) substrates pre-treated with Zn, Cu, and Ni coatings to tailor interfacial reactions and control the morphology of intermetallic compounds (IMC). Microstructural characterization revealed that each coating uniquely influenced the IMC evolution. Zn-coated MS developed a moderately thick (~185 µm) IMC layer dominated by Fe2Al5, FeAl3, and Fe4Al13 with tongue-shaped features, voids, and cracks, leading to poor bonding strength (~18 MPa). Cu coating promoted the thickest IMC layer (>290 µm), composed primarily of Fe2Al5 and FeAl5, along with localized Cu enrichment, resulting in intermediate shear strength (~36 MPa) due to heterogeneous and brittle interfacial phases. Ni coating produced the thinnest (~135 µm), continuous IMC layer, effectively restricting interdiffusion through its barrier role and thus yielding the highest shear strength (~56 MPa). Across all systems, a fracture occurred at the IMC interface and propagated into the AA side, confirming IMC brittleness as the critical factor governing failure. The findings demonstrate that Ni provides superior control of IMC growth compared with Zn and Cu, improving interfacial microstructure and joint strength.