Trade-off between dynamic recrystallization and material ejection during ultrasonic welding of cylindrical cell current collector plate and positive terminal

Ultrasonic welding was successfully carried out to join the current collector plate and positive battery terminal of a cylindrical battery cell by optimizing weld energy into safe energy input by varying various weld variables. The success of these welds is justified by balancing the occurrence of desired dynamic recrystallization and undesired material ejection. The welds were carried out on dissimilar aluminum alloys of 1060 of 0.2 mm and 3003 of 3 mm thicknesses at a constant frequency of 20 kHz and welding time of 0.12 s by varying weld amplitude and pressure. An in-depth electron and laser confocal analysis revealed that the dynamic recrystallization increased with increasing weld energy input. However, exceeding 20 J of energy input, the enhancement of DRX failed to boost the joints’ peak load (PL) consistently due to excess material ejection, and below 9 J, the joints exhibited nugget shear failure, defining a region of safe energy input (SEI) experimented with weld parameter window. The correlation of PL deterioration with other weld attributes, as analyzed by laser confocal microscopy, high-speed camera observation accompanied with scanning electron microscopy revealed that bond depth achieved over 340 µm enforces an excess amount of material ejection in the form of particles and solid strips, reducing the effective joint length and causing degradation of PL even though DRX occurred.