Interfacial reaction modification in Al/steel joints using a Si-rich interlayer during wire-based friction stir additive manufacturing

Joining low-Si 5B06 Al alloy to steel is limited by brittle Fe-Al intermetallic compounds. Here, a Si-rich 4043 Al interlayer (4.5 wt.% Si) was locally introduced between 5B06 Al alloy (0.24 wt.% Si) and 316L stainless steel during wire-based friction stir additive manufacturing. Compared with a direct 5B06/316L joint showing interfacial cracking, the 5B06/4043/316L joint exhibited a sound interface, a retained Si-rich transition region, and a locally observed ∼200 nm reaction layer. Transmission electron microscopy/energy-dispersive X-ray spectroscopy revealed interfacial Si enrichment and supported the local identification of α-Al ₁₅ (Fe, Mn) ₃ Si ₂ -type reaction products. The 5B06/4043/316L joint exhibited an ultimate tensile strength of 230 ± 10 MPa and a fracture strain of 3.7 ± 0.5%, reflecting the combined effects of the interlayer design, including Si-assisted interfacial reaction and transition-region modification.