Effect of nickel interlayer thickness on intermetallic compound formation and interfacial integrity in pulsed laser welding of aluminum and copper

Laser welding of aluminum (Al) and copper (Cu) is widely used in battery manufacturing due to its low heat input and precise control. However, the significant thermal, mechanical, and metallurgical differences between Al and Cu often promote the formation of brittle intermetallic compounds (IMCs), leading to microcracks, voids, and reduced joint integrity. To address this, nickel (Ni) was introduced as an interlayer by electroplating on Al sheets. This study investigates the effect of varying Ni plating thicknesses (0.8–3.5 µm) and configurations (top-side, bottom-side, and both sides) on IMC formation and overall joint quality in Al-Cu joints produced using a nanosecond pulsed laser. Key parameters, including weld morphology, thermal behavior, shear strength, electrical resistance, and IMC characteristics, were examined. Microstructural analysis revealed that Ni effectively suppresses excessive IMC growth and minimizes defects. Both-side plating with a 1.5 µm Ni layer yielded the thinnest IMC layer (0.24 µm versus 1.86 µm in non-plated joints), correlating with an 11.1% increase in shear strength, 23.7% improvement in elongation, and 14.6% reduction in electrical resistance. These findings highlight the critical role of Ni interlayers in controlling IMC evolution and improving the microstructural integrity of Al-Cu laser welds.