The battery performance of electric vehicles depends on the density and capacity of the battery; thus, the battery cells must be assembled in as many layers as possible. Electric vehicle batteries are typically composed of several cells which form modules connected by busbars, with dozens of modules manufactured as battery packs. The ultrasonic metal welding (UMW) technology is applied to such multilayered foil welding. This study analyzed UMW to ensure the weldability of multilayered Cu foils and a Ni-plated Cu strip in lithium-ion battery cells through various approaches. In UMW, the effect of the alignment on weld production and quality were examined through the energy and mechanical performance of the weld by conducting comparative experiments on the alignment of the horn and anvil. Additionally, the effects of UMW process parameters, such as the welding pressure, amplitude, and welding time, were statistically analyzed. The weldability evaluation and characteristic analysis were performed based on these variables. Furthermore, the cross-sectional shapes and microstructure behavior of the Ni layers were analyzed based on the weld quality.

In this study, we present the energy absorption capabilities achieved through the application of hybrid lattice structures, emphasizing their potential across various industrial sectors. Utilizing Ti-6Al-4V and powder bed fusion (PBF) techniques, we fabricated distinct octet truss, diamond, and diagonal lattice structures, tailoring each to specific densities such as 10, 30, and 50%. Furthermore, through the innovative layering of diverse lattice types, we introduced hybrid lattice structures that effectively overcome the inherent energy absorption limitations of single-lattice structures. As a result, we conducted a comprehensive comparison between single-lattice structures and hybrid lattice structures of equal density, unequivocally showcasing the latter’s superior energy absorption performance in terms of compression. The single-lattice structure, OT, showed an energy absorption of 42.6 J/m³, while the reinforced hybrid lattice structure, OT-DM, represented an energy absorption of 77.8 J/m³. These findings demonstrate the significant potential of hybrid lattice structures, particularly in energy-intensive domains such as shock absorption structures. By adeptly integrating various lattice architectures and leveraging their collective energy dissipation properties, hybrid lattice structures offer a promising avenue for addressing energy absorption challenges across diverse industrial applications.

In the application of Ti-6Al-4V to aerospace structural components, when welding thick plates similar of the thickness of the components, microstructure and hardness gradients emerge between the base material (BM) and the joint. This leads to the issue of significant stress concentration in the BM under tensile stress. To address this problem through post-welding heat treatment, this study conducted heat treatments at temperatures both below (mill annealing, MA) and above the beta-transus temperature (beta annealing, BA) on electron-beam weldments of 18 mm thickness Ti-6Al-4V plates. Subsequently, microstructures and hardness were analyzed at different depths from the upper surface and areas (fusion zone (FZ), heat-affected zone (HAZ), and BM), and tensile properties were measured at various depths. The results indicated that α′ observed in FZ and HAZ was resolved through both MA and BA. Particularly after BA, the microstructural gradient that persisted even after MA completely disappeared, resulting in the homogenization of widmanstätten α + β. Consequently, after BA, the hardness gradient in each zone also disappeared, and the tensile strength was higher than in just-welded and MA heat-treated plates.