High-brightness laser welding with beam wobbling: Achieving high-strength Al/Steel joints for battery busbars

• A cost-effective alternative to Cu busbars reduces weight/cost by 70 %/60 %. • Mechanically strong, fatigue-tested Al-steel overlap welds. • Optimisation of spatial and temporal distribution of laser energy yields stronger welds. • Optimum welds show Fe-rich IMCs and Al-Fe₄Al₁₃ eutectic phases. Laser welding of aluminium tabs to nickel-plated interstitial-free (IF) steel was investigated using a high-brightness, single-mode laser with beam wobbling. The influence of interaction time, controlled by wobble amplitude and traverse speed, regulating energy distribution on weld microstructure and mechanical properties was systematically studied. Short interaction times (<25 µs) and large inter-wobble distances (>150 µm) minimized intermetallic compound (IMC) formation and maximized weld strength. Optimizing these parameters (wider wobble amplitudes of 0.6–0.8 mm and faster speeds of 75–100 mm/s) suppressed IMC-induced cracking, resulting in microstructures containing Fe-rich IMCs and Al-Fe₄Al₁₃ eutectic phases. Conversely, lower wobble amplitudes (<0.6 mm) and slower speeds (50–75 mm/s) promoted crack-prone Al-rich Fe₂Al₅ phases. Optimized welds exhibited excellent fatigue performance, withstanding 1 million cycles at 175 N, demonstrating the potential for using lighter, cost-effective aluminium busbars in battery interconnect applications.