Interfacial microstructure and mechanical properties of Al/Ti dissimilar joints fabricated via friction stir welding

Dissimilar joints of AA6061 and Ti6Al4V alloys were obtained via friction stir welding using W-Re pin tools. The intermetallic compounds (IMCs) and the deformation of Ti matrix were depicted from the interfaces as probe length increased, which could be attributed to the promotion of interfacial pressure and temperature. TiAl3 was formed at all the Al/Ti interfaces in this study, and TiAl formed in the joint welded by 3.3 mm probe following TiAl3 for lower activation energy. Due to the increase of free energy caused by the solid dissolution of Ti in Al matrix, TiAl3 nanoparticles precipitated in the diffusion layer, which could be depicted at the Al side of the interface with an overall Ti concentration ranging from 3 to 5 (At. %). It is indicated that the amount of IMCs increased in the joints with increasing probe length. The mechanical properties of the joints were significantly affected by the interfacial microstructure. The shear strength and elongation reached the maximums of 147.5 MPa and 4.1% respectively using the pin tool with 3.1 mm probe. Cleavage fracture gradually dominated the fracture of the joints as the probe length increased, which could be attributed to the formation of intermetallic compounds. •The interface evolution is systematically studied with the exact interfacial pressure and temperature.•The formation of interfacial phases are identified by TEM and discussed by thermodynamics and kinetics.•The shear strength of the welds is optimized to be 147 MPa, which is 32% higher than former studies at least.•The relationship between the interfacial microstructure and fracture mechanism is revealed.