Microstructure and bonding mechanism of Al/Ti bonded joint using Al–10Si–1Mg filler metal

The microstructures and liquid state diffusion bonding mechanism of cp-Ti to 1050 Al using an Al–10.0wt.%Si–1.0wt.%Mg filler metal with 100 μm in thickness have been investigated at 620 °C 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, scanning electron microscopy and EDS. The interfacial bond strength of Al/Ti bonded joints was measured by the single lap shear test. The results show that the bonding at the interface between Al and filler metal proceeds by wetting the Al with molten filler metal, and followed by removal of oxide layer on surface of Al. The interface between Al and filler metal moved during the isothermal solidification of filler metal by the diffusion of Si from filler metal into Al layer. The interface between Al and filler metal became curved in shape with increasing bonding time due to capillary force at grain boundaries. The bonding at the interface between Ti and filler metal proceeds by the formation of two different intermetallic compound layers, identified as Al5Si12Ti7 and Al12Si3Ti5, followed by the growth of the intermetallic compound layers. The interfacial bond strength at Al/Ti joint increased with increasing bonding time up to 25 min at 620 °C. However, the interfacial bond strength of Al/Ti joint decreased after bonding time of 25 min at 620 °C due to formation of cavities in Al near Al/intermetallic interfaces.