Solid-state Additive Friction Stir Deposition (AFSD) of dissimilar Al Cu materials with FSP-enabled interface design for improved metallurgical bonding

Dissimilar aluminum‑copper material systems are widely used in thermal management, electrical interconnects, and multifunctional structural components, but their reliable fabrication remains difficult due to large differences in physical properties and the formation of brittle intermetallic compounds (IMCs). Additive Friction Stir Deposition (AFSD), a solid-state additive manufacturing process, mitigates many of these challenges by enabling metallurgical bonding through frictional heating and severe plastic deformation (SPD) below the melting point, thereby avoiding melting-related defects. In this study, AA6061 was deposited onto Cu substrates featuring two interface geometries (flat and dovetail) and two surface conditions (with and without friction stir processing, FSP), yielding four distinct processing conditions. Comprehensive material and mechanical characterization revealed that IMC formation primarily consisted of Al₂Cu , Al 3 Cu AlCu , and Al 4 Cu 9 , with their thickness and continuity governed predominantly by the imposed thermomechanical history rather than the interface geometry. Microhardness profiles remained relatively uniform across each processing condition with only modest interfacial hardening corresponding to localized IMC accumulation. Mechanical testing showed that flat AFSD interface exhibited limited strain capacity and brittle, interface-dominated failure; dovetail interfaces permitted greater global displacement due to their geometric compliance but did not produce true ductile behavior; and FSP-modified interfaces (flat and dovetail) demonstrated the most balanced mechanical performance through enhancement of diffusion and interfacial refinement, delaying crack initiation, redistributing strain, and promoting mixed ductile-brittle fracture behavior. Overall, the results demonstrate that enhanced metallurgical bonding and printability of Al Cu joints in AFSD require the coupling of thermomechanical preprocessing and interface architecture, providing a pathway for multi-material components in advanced engineering applications.