Processing of AA6101/C11000 friction stir welds with hybrid interlayers

Friction stir welding is a promising solid-state technique for joining dissimilar AA6101 aluminum and C11000 copper. However, turbulent material flow and brittle Al–Cu intermetallic compounds often limit joint performance. This study systematically examines the combined influence of tool pin profile and a hybrid Ag–Zn interlayer (0.2 mm Ag + 0.2 mm Zn foils) on material flow, intermetallic formation, and mechanical behavior. Joints produced using a plain taper pin (PTP) exhibited smoother material flow and improved intermixing compared to taper-threaded pin. The Ag–Zn interlayer effectively suppressed brittle Al–Cu IMCs and promoted ductile phases such as Al–Zn, Ag–Al, and Cu–Zn. The optimized PTP + Ag–Zn joint achieved a refined stir zone, 30–40% higher hardness than AA6101, and a 75% increase in tensile strength (~156 ± 10 MPa), corresponding to ~79% joint efficiency. Fractography confirmed a transition to predominantly ductile fracture, demonstrating enhanced joint integrity for lightweight electrical applications.