The microstructures and liquid state diffusion bonding mechanism of cp-Ti to pure Al using an Al-10.0wt%Si-1.0wt%Mg insert metal with 100μm in thickness have been investigated at 620℃ under 1 × $10^{-4}$ torr. The effects of bonding process parameters on microstructure of bonded joint have been analyzed by using an optical microscope, AES, SEM and EPMA. The interfacial bond strengths of Al/Ti bonded joints were measured by the single lap shear test. The results show that the bonding at the interface between Al and insert metal proceeds by wetting the Al with molten insert metal, and followed by removal of oxide layer on surface of Al. The interface between Al and insert metal moved during the isothermal solidification of insert metal by the diffusion of Si from insert metal into Al layer. The interface between Al and insert metal became curved in shape with increasing the bonding time due to capillary force at grain boundaries. The bonding at the interface between Ti and insert metal proceeds by the formation of two different intermetallic compound layers, identified as $Al_5Si_{12}Ti_7$ and $Al_{12}Si_3Ti_5$, and followed by the growth of the intermetallic compound layers. The interfacial bond strength at Al/Ti joint increased with increasing the bonding time up to 25 minutes at 620C. However, the interfacial bond strength of Al/Ti joint decreased after bonding time of 25 minutes at 620℃ due to formation of cavities in Al near Al/intermetallic interfaces.
The microstructures and solid state diffusion bonding mechanism of 1060 Al and Zr has been investigated in the temperature range from 400 to 500℃ with increasing the pressure from 5 MPa to 80MPa and pressure time from 1 to 180 minutes. When the pressure was applied in the initial stage under the experimental conditions, the asperities formed on the surface were plastically deformed and the oxide layers were damaged. When the bonding proceeded, the parts that were not contacted in the initial stage contained thin, lenticular voids. As the bonding time increased, the shape of voids was changed into spherical in order to reduce the interfacial energy. Finally, these spherical voids are gradually eliminated by creep deformation and duffusion process. The bond strength increased with increasing the bonding temperature, pressure and bonding time. Three methods were proposed to improve the bonding characteristics. Firstly, bond strength increased by disruption of surface oxide by increasing pressure. Secondly, the bond strength increase with increasing the surface roughness by damage of surface oxide and strong mechanical locking phenomena. Finally, bond strength increased at the level of 80% of strength of Al base metal by formation of intermetallic compounds by interdiffusion between Al and Zr. From the results of the heat treatment to 400 hours at the range of 450℃- 550℃, two phases, i.e., $Al_3Zr$ phase and $Al_2Zr$ phase, was characterized by performing EDS analysis and XRD experiments. The growth of $Al_3Zr$ intermetallic compound was observed as an important phenomenon to understand the reaction at the interface between Zr and Al. The growth rate of $Al_3Zr$ intermetallic compound was controlled by diffusion process and the activation energy for growth of $Al_3Zr$ phase was 214 kJ/mol. It was suggested that the growth mechanism of $Al_3Zr$ phase was diffusion of Zr in Al. In order to analyse the bonding characteristics, the modeling for solid state diffusion bonding was suggested and it was possible to predict the bonding process time from these model. Assumption was follows; Al was plastically deformed by ridge to ridge contact and cylinrical pores were uniformly distributed along the bonded interface. And the pore closure was accomplished by a combination of creep deformation by hystrostatic stress around pores and diffusion process. From this model, it was possible to predict the bonding time with increasing the bonding area fraction. And the theoritical results were in good agreement with the measured results.
