A method for attaching a metal ring (4) in a bore (3) of a frame (2) made of a different metal, wherein: the ring (4) is set in the bore (3) by way of high-energy forming suitable for urging an outer surface of the ring against the bore (3) with a speed capable of driving out any impurity from an interface between the ring and the frame; the interface between the ring (4) and the frame (2) is heated to a temperature and for a length of time that are determined in accordance with the respective materials of the ring and the frame such as to obtain diffusion welding between the outer surface of the ring and the bore. A single-turn coil for magnetic forming carried out by the method is also described.