Process optimization and characterization of ultra-thin dissimilar sheet material joints for battery applications using ultrasonic welding

The present work explored the application of ultrasonic welding process for an acceptable robust joint of dissimilar ultra-thin sheet materials. The joining process was carried out with two material combinations for potential battery application, and these were aluminum (grade AA1050) of 0.2 mm thickness with copper (grade C101S) of 0.3 mm thickness and C101S with nickel-coated steel of 0.3 mm thickness. The input parameters affecting the weld quality were identified, and the optimization of these parameters was carried out through response surface methodology to maximize the output responses of lap shear and T-peel strength. The cross section of weld samples was characterized using optical microscopy, SEM and microhardness tests in order to understand the bond mechanism. It was observed that the bond strength was a combination of metallurgical bonding, mechanical interlocking and inter-metallic diffusion. Higher hardness was found in the region where the sonotrode tip contacted the sample, indicating excessive plastic deformation. However, the hardness near the valley region was similar or lower compared to the hardness of parent material due to heat generation and subsequent thermal softening. The strength and microscopy characterization data were used to establish a relationship between the mode of failure and the physical attributes of the weld