Microstructure and mechanical properties of Cu/steel dissimilar joints

Different groove types and transition fillers were designed to butt join explosion-welded Cu/steel bimetallic plate. Three kinds of transition fillers, the ERNi-1, ERNiCu-7 and ERNiCrMo-3, were applied. The transition welds were consisted of γFe and Cu(s,s) compounds featured by dendrite morphology. The diffusion of Cu element into the steel welds resulted in the severe cracking. To this end, groove type B was designed, where steel plate was joined firstly and the Cu plate was joined lastly. In this case, Cu element distribution was kept at a minimum in the steel welds and defect-free welded joints were obtained. Ni2Si intermetallics were precipitated in the Cu weld metal. The transition welds showed higher microhardness than the base metals and steel welds. The tensile strength of the butt welded joints reached 436 MPa and 425 MPa, close to that of the bimetallic plate. Simple models were proposed to reveal the evolution of typical microstructures in the resultant weld metals.