Effect of Annealing on the Interfacial Structure of Aluminum-Copper Joints

Abstract

The aim of this study is to investigate the structure development and growth kinetics of the interfacial structure of cold roll bonded Al/Cu bimetal sheet. An interfacial structure is developed during the annealing process. The characteristics of the constituent phases at the interface of Al/Cu bimetal are studied by means of scanning electron microscope (SEM), X-ray diffraction (XRD) and transmission electron microscope (TEM). The results indicate that an obvious multi-layers interdiffusion structure is developed at the Al/Cu interface. The diffusion layer is consisted of four intermetallic compounds; Al₂Cu, AlCu, Al₃Cu₄ and Al₄Cu₉. The growth of these intermetallics during annealing can be achieved by the diffusion process. The activation energies of Al₂Cu, AlCu + Al₃Cu₄, Al₄Cu₉ and the total intermetallic layer are found to be 97.504, 107.46, 117.52 and 107.85 kJ/mol, respectively. These intermetallics generally possess higher hardness values than those of the corresponding base metals. AlCu and Al₃Cu₄ exhibit much higher hardness than that of Al₂Cu and Al₄Cu₉, which implies lower fracture toughness. The observation of crack propagation paths shows that fracture mainly occurs in the intermetallic compound layers of AlCu and Al₃Cu₄, which are located between Al₂Cu and Al₄Cu₉.