In this study, the ultrasonic welding process between two dissimilar metals, aluminum an‎d copper, was investigated using a nickel–phosphorus (Ni–P) interlayer deposited by the electroless plating method. Direct bonding of aluminum to copper typically leads to the formation of undesirable intermetallic compounds, which reduce joint quality; to address this issue, a Ni–P interlayer was employed. The main objective of this research was to eva‎luate the effect of the presence an‎d varying thicknesses of the Ni–P interlayer (0, 2, 6, an‎d 14 μm) on the joint quality an‎d overall performance from mechanical, electrical, an‎d corrosion perspectives. This study was conducted using an experimental an‎d analytical approach. First, the optimal ultrasonic welding process parameters were determined through preliminary tests an‎d an assessment of joint quality. Then, samples with Ni–P interlayers of the specified thicknesses were welded under the optimized conditions. After welding, a series of characterization tests were performed to analyze the behavior an‎d structure of the joints. To examine the microstructure, bonding mechanism, an‎d fracture mode, optical microscopy (OM), scanning electron microscopy (SEM), an‎d energy-dispersive X-ray spectroscopy (EDS) were employed. The investigations revealed that the presence of the Ni–P interlayer significantly increased the weld linear density an‎d uniformity of the joint interface. The bonding mechanism, penetration, an‎d mechanical interlocking were identified. Additionally, all samples exhibited fracture at the joint interface. Tensile tests indicated that the mechanical strength of the joints increased with the Ni–P interlayer thickness, reaching a maximum in the sample with a 14 μm interlayer. On the other han‎d, the electrical resistance of the joints decreased in the presence of the Ni–P interlayer; however, at higher thicknesses, the formation of intermetallic compounds led to an increase in electrical resistance again, with the lowest resistance observed at 2 μm thickness. For corrosion assessment, potentiodynamic polarization tests were conducted in a 0.1 M sodium chloride (NaCl) electrolyte. The results demonstrated that using the Ni–P interlayer improved the corrosion resistance of the joints. A combined analysis of mechanical, electrical, an‎d corrosion properties indicated that a 14 μm Ni–P interlayer provided the most balanced set of properties an‎d was identified as the optimal thickness. Therefore, employing a Ni–P interlayer in ultrasonic welding of aluminum to copper not only enhanced bonding an‎d joint structure but also improved the mechanical, electrical, an‎d corrosion performance of the joints. Considering the importance of tab-to-tab connections in lithium-ion batteries, the findings of this study have practical implications for improving mechanical strength, electrical conductivity, an‎d corrosion resistance.

قاسم عظيمي روئين

امين اله محمدي

عبدالمجيد اسلامي , علي اشرفي