Formation mechanism of in situ Al3Ti in Al matrix during hot pressing and subsequent friction stir processing

In situ Al3Ti/Al composites were fabricated by a combination of vacuum hot pressing (VHP) and friction stir processing (FSP). The formation mechanism of the Al3Ti and the effect of VHP and FSP parameters on the resultant microstructure and mechanical properties were investigated. The Al3Ti formed due to the reactive diffusion between Al and Ti during VHP, and the number of Al3Ti particles increased with increasing the temperature and holding time of the VHP. FSP not only induced the Al–Ti reaction, but also resulted in significant refining of the Al3Ti, thereby creating a homogeneous distribution of Al3Ti particles in the Al matrix. These microstructural changes led to significant improvement in the tensile properties of the in situ Al3Ti/Al composite. However, the change trends of the tensile properties of the FSP samples were dependent on the extent of the Al–Ti reaction during VHP.

► Al3Ti formed due to reactive diffusion during vacuum hot pressing (VHP).
► Friction stir processing (FSP) induced the Al–Ti reaction.
► FSP refined the Al3Ti blocks and dispersed Al3Ti uniformly in the matrix.
► The tensile strength was improved substantially by FSP.
► The optimal parameters of VHP and FSP were obtained.