Effect of friction stir processing (FSP) on microstructure and properties of Al–TiC in situ composite

Aluminium based in situ composites have many advantages over their conventional counterparts. However, a major problem in such composites is the segregation of the in situ formed particles at the grain boundaries. In this study, it has been shown for the first time that friction stir processing (FSP) can be used effectively to homogenise the particle distribution in Al based in situ composites. An Al-5 wt.% TiC composite was processed in situ using a mixture of K2TiF6 and graphite powders in aluminium melt. Friction stir processing was employed on the as-cast composite to uniformly distribute the TiC particles in the Al matrix. The composite was subjected to single and double pass FSP and its effect on the microstructure and properties was evaluated. A single pass of FSP was enough to break the particle segregation from the grain boundaries and improve the distribution. Two passes of FSP resulted in complete homogenization and elimination of casting defects. The grain size was also refined after each FSP pass. This led to significant improvement in the mechanical properties. The novel feature of the composite is that while the strength and hardness improved substantially after FSP, the ductility was not compromised.