Characterization of diffusion-bonded joint between AI and Mg using a Ni interlayer

Aluminum and magnesium were joined through diffusion bonding using Ni interlayer. The micro- structure and mechanical performance of the A1/Ni/Mg joints at different temperatures was investigated by means of scanning electron microscope （SEM）, electro-probe microanalyzer （EPMA）, X-ray diffraction （XRD）, Vickers hardness testing, and shear testing. The results show that the addition of Ni interlayer eliminates the formation of Mg-A1 intermetallic compounds and improves the bonding strength of the A1/Mg joints. The AI/Ni/Mg joints are formed by the diffusion of A1, Ni and Mg, Ni. The microstructure at the joint interface from A1 side to Mg side is A1 substrate/A1-Ni reaction layer/Ni interlayer/Mg-Ni reaction layer/Mg substrate multilayer structure. The mi- crohardness of the Mg-Ni reaction layer has the largest value of HV 255.0 owing to the existence of Mg2Ni phase. With the increase of bonding temperature, the shear strength of the joints increases firstly and then decreases. The A1/Ni/Mg joint bonds at 713 K for 90 min, exhibiting the maximum shear strength of 20.5 MPa, which is greater than that of bonding joint bonded directly or with Ag interlayer. The fracture of the joints takes place at the Mg- Ni interface rather than the A1-Ni interface, and the frac- ture way of the joints is brittle fracture.