Al/Cu bimetallic electrical joints: state-of-the-art with emphasis on continuous-drive friction welding

Abstract

The increasing use of aluminum conductors while retaining copper terminals has increased the need for reliable Al/Cu transitions. Mechanical connectors remain practical, but their long-term performance depends on stable pressure-controlled contact despite oxidation, corrosion, thermal expansion mismatch, creep, stress relaxation, and fretting. Metallurgical transitions reduce this dependence. Continuous-drive friction welding (CDFW) is particularly attractive for cylindrical components because it is rapid, filler-free, and avoids bulk melting. This review relates CDFW parameters to material transfer, interface morphology, recrystallization, intermetallic-compound (IMC) formation, radial heterogeneity, electrical behavior, mechanical properties, fracture, and thermal exposure. Insufficient heat input produces incomplete bonding, whereas excessive heat input promotes softening, material loss, and IMC growth. Optimized short-cycle CDFW can produce complete bonding with approximately 0.5 μm Al₂Cu while retaining more than 92% of the theoretical Al/Cu conductivity and approximately the tensile strength of the Al base material. However, IMC thickness alone cannot describe joint integrity because phase composition, continuity, residual stress, radial distribution, and adjacent microstructure also influence fracture. Future development should therefore focus on phase-specific, spatially resolved, and service-life-oriented interface engineering.