Interlocking Interfaces with Nanostructured Intermetallics Enable Enhanced Performance in Aluminum-Copper Hybrid Rotors for Next-Generation Electric Motors

Electric drives and other vehicle motors have renewed interest in aluminum-copper (Al-Cu) hybrid rotors, which combine aluminum’s low weight with copper’s superior conductivity. Die-casting of Al-Cu rotors, however, suffers from the formation of brittle intermetallic compound (IMC) layers that limit joint strength and long-term reliability. Here, we demonstrate for the first time-the use of friction stir welding (FSW) to fabricate Al-Cu hybrid rotor joints for induction motors. Optimized welding schemes produced robust metallurgical bonds, achieving pull-out loads of 3272 ± 60 N, approximately 20% higher than die-cast counterparts. Microstructural characterization by scanning transmission electron microscopy revealed nanoscale IMCs, primarily Al₂Cu and Al₄Cu₉, with Ni interlayers further refining interface chemistry and improving load capacity. Full rotor assemblies fabricated with the optimized FSW process sustained maximum loads of 185 kN, representing nearly a two-fold improvement in mechanical performance relative to conventional designs. Electrical resistance of FSW joints (14.9 ± 0.7 µΩ) was comparable to that of bimetallic Al-Cu joints, confirming their suitability for traction applications. By overcoming longstanding challenges in IMC formation and joint integrity, this study establishes FSW as a scalable and transformative manufacturing method for next-generation hybrid rotors, underscoring its promise as a pathway for enhancing electric motor performance and advancing the future of mobility.