Laser Welding of Dissimilar Aluminum/Copper Joints: A Review

Aluminum/copper (Al/Cu) laser-welded joints are increasingly used in lightweight and highly conductive interconnections, including battery tabs, busbars, and power modules. The pronounced differences between Al and Cu in thermophysical properties, optical absorptivity, and metallurgical compatibility promote the formation of Al–Cu intermetallic compounds (IMCs), heterogeneous reaction zones, pores, cracks, and lack-of-fusion defects. These microstructural features and defects can affect the load-bearing capacity, electrical resistance, current-induced temperature rise, and long-term stability of the joints. This review examines recent advances in interfacial reactions, weld-pool mixing, defect formation, process control, interlayer-assisted joining, process monitoring, and service reliability of laser-welded Al/Cu joints. The applicability of continuous-wave, pulsed, beam-oscillation, core–ring beam, short-wavelength laser, and external-field-assisted approaches is evaluated in relation to sheet thickness, stacking sequence, penetration requirements, electrical-resistance requirements, production cycle time, and interfacial gap. Multisensor monitoring can establish correlations between process signals and penetration depth, interfacial fusion width, or defect state. However, model performance should be validated using cross-sectional metallography, micro-computed tomography (μXCT), and service-performance data. Independent-weld validation and tests across processing conditions are needed to assess model transferability. Finally, a conceptual traceable quality-chain framework is proposed for Al/Cu electrical interconnections. The framework links processing parameters with interfacial microstructure, spatial defect distribution, effective current paths, and service-related performance drift, providing a basis for traceable quality assurance and reliability assessment.