This work investigates the benefits of having an aluminum (Al) busbar with welded copper (Cu) ends, and evaluates the force relaxation phenomena of a pre-loaded bolt joint on Cu versus Al, under cyclic thermal loading. The results show a force relaxation rate 50% lower in the Cu-bolted joint compared with the one in Al. The core of this research is the weldability analysis of Al-Cu butt joints made by friction stir welding (FSW). The materials are AA1050 H14/24 and Cu OF 04 with thickness of 6 mm. Temperature monitoring during the FSW cycle emphasize how heat generation depends mostly on local internal viscoplastic deformation. Tensile, bending, and microhardness tests were used to establish the mechanical properties. Optical microscope and scanning electron microscopy were used to characterize the microstructure. Joining mechanisms in the weld were investigated using energy-dispersive X-ray spectroscopy. The FSW resulted in 85% tensile strength efficiency compared to the Al base material, and 97% electrical conductivity efficiency compared to an ideal bimetallic component made of the same materials with no contact resistance. Electrical resistance of the FSW is 200 times lower than the electrical contact resistance between the Al-Cu materials while under high compressive force.