Thin-walled area elements are becoming increasingly popular and necessary in construction and various other industries. This trend is also accompanied by the need for development and research into joining methods that will ensure that the structures have an appropriate ratio of their load capacity to their weight. A commonly used method for joining thin metal elements is resistance welding, using the natural electrical resistance property of metals. The study examined the impact of the resistance welding current value on the quality and load capacity of the RSW weld. Lap joints with a single weld, using alternative current flow values during welding, were made. The joints were subjected to a static tensile test. Load capacities of the analyzed joints and force-displacement graphs were obtained. A numerical analysis of joints with different weld diameters was also carried out. Plastic deformation graphs were obtained in the cross-section through the center of the weld and the distribution of plastic deformations throughout the sample. As the weld diameter increases, the load capacity of the joint increases and the plastic deformation decreases. However, the use of excessive current flow may cause molten metal splash and reduce the strength of the joint.