Evaluation of intermetallic compound layer at aluminum/steel interface joined by friction stir scribe technology

Highlights: • A theoretical model of AlFe intermetallic compound formation during friction stir welding of Al/steel is presented. • Conventional Effective Heat of Formation model was modified for predicting sequence of intermetallic compound formation. • Intermetallic compound thickness distribution along welded Al/steel interface was correlated to scribe trace. • Defect-free lap welded joints of Al 6022-T4 alloy and DP600 steel was achieved with an optimum joint efficiency of ~97%. -- Abstract: Heat input and high strain rate deformation during friction stir welding of aluminum and steel resulted in the diffusion-based formation of a Fe_xAl_y intermetallic compound (IMC) layer. Compared with conventional friction stir welding tools, a friction stir scribe tool can reduce heat input significantly limiting the IMC layer thickness (~100–750 nm). Friction stir scribe joined lap joints fractured either through the welded interface or within the base aluminum alloy on the loading side, depending on IMC layer thickness during tensile lap shear testing. In addition, a modified effective heat of formation model predicted that Al₁₃Fe₄ formed first at aluminum/steel interface and, during welding process, was substituted by Al₅Fe₂ with local silicon enrichment, which was verified via microstructural characterization.