Abstract: The rapid solidification welding of melt-spun Cu-x%Sn(x=7, 13.5, 20) alloy foils is conducted by a micro-type capacitor discharge welding machine and the microstructural morphology of joint is investigated.The cooling rate of micro nugget is calculated and the formation of porosity in nugget is analyzed theoretically.The results indicate that the capacitor discharge welding can realize the rapid solidification welding of melt-spun Cu-Sn alloy foils.The microstructure of joint is characterized by rapid solidification which consists of fine and homogeneous equiaxed grains.The cooling rate of nugget is up to 10⁷K/s and the welding period is merely 15.5 μs.Therefore, the joint microstructure is in accordance with the rapidly solidified alloy foils.The main welding defect is porosity.With the increase of Sn content, the porosity of nugget increases.