Microstructure and mechanical properties of Al-Cu joints diffusion-bonded with Ni or Ag interlayer

The heterogeneous joint constituted by Al and Cu were diffusion-bonded with Ni or Ag interlayer under different bonding parameters, which was compared with directly bonded Al-Cu joints to analyze the effects of the different intermetallic compounds (IMCs) produced at the joining interface on the joint mechanical properties. The joint microstructure was analyzed by scanning electron microscope (SEM), the compositions profiles across the joining interface were measured by energy dispersive spectroscopy (EDS), and the mechanical properties of joints were evaluated by hardness, indentation fracture toughness, and tensile test. The experiment results demonstrated that the Al-Ag-Cu and Al-Cu joints couldn't avoid the crack due to the thick, hard and brittle IMCs layer formed at the joining interface, while, the thickness of the IMCs in the Al-Ni-Cu joint is less than 3.8 μm, this thin IMCs layer ensured that the joining interface exhibited the lowest hardness and brittleness in microscales, so the Al-Ni-Cu joint was free of cracks not only after bonding but also under the load of indentation fracture toughness test. The tensile test indicated that the Al-Ni-Cu joint had the highest tensile strength (47 MPa), which was bonded with 50 μm thick Ni interlayer at 10 MPa, 520 °C, 60 min.