Systematic study of the effect of K2TiF6 flux content on the microstructure and mechanical properties of Al-B4C composites

Al-B4C Metal matrix composites (MMCs) possess several attractive properties such as high hardness, superior resistance to impact and wear, excellent resistance to chemical agents, neutron absorption capability, etc. While stir-casting is the most economic route for fabricating these MMCs, this requires mitigating the poor wettability and improving the interfacial bonding between B4C particles and Al-melt. Inorganic K2TiF6 salts are generally added to the Al-melt as fluxing agents to enhance wettability. However, a systematic study of the effect of K2TiF6 flux content on the microstructure and mechanical properties of Al-B4C MMCs is still lacking. This work intends to fill this gap. Al-alloy 6061 reinforced with 6 wt% B4C and different amounts of K2TiF6 flux additions (40 wt%, 70 wt%, and 100 wt% with respect to the amount of B4C) were fabricated by combined stir-casting + squeeze -casting. A detailed analysis of the microstructure and mechanical properties of the composites was performed both in the as-cast condition and after T6 heat treatment. It was ascertained that the retention efficiency of the B4C particles in the matrix improved with increasing flux content due to an improvement in the interfacial bonding through the formation of Ti-rich intermetallic phases, and this resulted in an increase in the strength and hardness of the MMCs. Several mechanisms such as grain refinement, load transfer, coefficient of thermal expansion mismatch, and stiffness mismatch contributing to the strengthening of the MMC have been considered in detail to determine their relevance in the fabricated composites.