Solid-State Ti-Al Metallurgical Bonding via Oscillatory Shear-Strain-Assisted Metal Deposition

: Fusion-based dissimilar-metal joining of titanium (Ti) and aluminum (Al) is persistently limited by brittle intermetallic compounds (IMCs) formed at Ti-Al interfaces, which promote cracking, embrittlement, and premature failure. To overcome such challenges, the present study demonstrates a novel oscillatory shear-strain-assisted solid-state deposition technique that achieves Ti-Al metallurgical bonding below the melting point without detectable crystalline IMCs in the examined regions. High-frequency acoustic energy (38.5 kHz; ∼3.5 μm peak-to-peak displacement) was transmitted through an oscillatory shear-strain transfer tool to plastically deform and join commercially pure titanium (Cp-Ti) wire voxels onto an AA6061-T6 substrate heated to ∼300 °C. Interfacial sliding and severe plastic deformation disrupted and redistributed native oxides, exposed fresh metallic surfaces, and generated intimate contact. Metallurgical bond formation is attributed to the combined effects of deformation-driven mechanical intermixing and acoustic energy enhanced defect-mediated mass transfer. Cross-sectional analysis revealed significant plastic deformation of the deposited Cp-Ti with strain values up to ∼0.47. Tensile testing of AA6061-T6 specimens with a deposited Cp-Ti layer showed a ∼30% increase in ultimate tensile strength along the printing direction compared to the reference AA6061–T6 samples. High-resolution STEM-EDS revealed a dense Ti-Al interface with a confined ∼28-60 nm compositional-transition zone, while nano-beam electron diffraction detected no crystalline Ti-Al IMCs within the characterized regions. These findings support a coupled solid-state bonding mechanism involving mechanical intermixing and defect-assisted mass transport without evidence of interfacial melting. This study establishes a thermal-fusion-free, solid-state pathway for Ti-Al metallurgical bonding that avoids IMC formation, providing a foundation for dissimilar Ti-Al joints.