Abstract: Large-scale components of steel and aluminum alloys (Fe-Al) with high bonding strength are highly needed from space exploration to the fabrication of transportation systems. The formation of detrimental intermetallic compounds at the Al-Fe interface has limited the application range of the Fe-Al components. The modified friction stir additive manufacturing was developed for fabricating large-scale Fe-Al components with homogenously distributed interfacial amorphous layers rather than detrimental intermetallic compounds. The interfacial amorphous layers comprised an Mg-O rich amorphous layer < 20 nm in thickness and an Al-Fe-Si amorphous layer < 120 nm in thickness. The interfacial amorphous layers exhibited high thermal stability and did not change even after the post-processing heat treatment of heating at 500 °C for 20 min and aging at 170 °C for 7 h. The tensile strengths of the Fe-Al tensile specimens were increased from 160 to 250 MPa after the application of the post-processing heat treatment. The fracture occurred in the aluminum alloys instead of at the dissimilar metal interface, demonstrating that high bonding strength at the Al-Fe interface was enabled by the formation of homogenously distributed interfacial amorphous layers.

Key words: Modified friction stir additive manufacturing, Friction stir welding, Interfacial amorphous layer, Post-processing heat treatment, High joint strength