Enhancing strength-ductility synergy and mechanisms of Al-based composites by size-tunable in-situ TiB2 particles with specific spatial distribution

The increase in strength usually accompanies by the sacrifice of ductility in the composites. This work proposed a strategy of design and synthesis of in-situ TiB2 particles to effectively tailor the microstructures and to enhance the mechanical performance of Al–Si-based composites. The tuning mechanisms for size and morphology of TiB2 particles were investigated by combustion synthesis in the Al–Ti–B reaction system. The nano/submicron-sized TiB2 particles with desirable morphology were then specially selected to construct high-performance Al–Si-based composites. Thanks to the strong interface bonding with a low crystallographic mismatch, TiB2 particles significantly refined the primary α-Al dendrites, eutectic Si and θ’ precipitates in the composites, which were 79.2%, 51.9% and 37.6% respectively smaller than those of the matrix. Numerical modeling results suggested that submicron-sized TiB2 particles were more likely to be engulfed or serve as heterogeneous sites while nano-sized TiB2 particles would be repulsed to the solid/liquid interface to physically restrict the growth of α-Al dendrites. The strength-ductility trade-off dilemma was broken therefore superior mechanical properties were obtained in the composites. This work provides a novel perspective for manipulating Al–Si-based alloys in terms of avoiding poisoning and achieving microstructural refinement and outstanding strength-ductility synergy. •Novel TiB2 particles were designed and synthesized to enhance the performance of Al–Si-based composites.•The size and morphology tuning mechanisms of in-situ TiB2 particles are revealed in the Al–Ti–B reaction system.•Nano/submicron-sized TiB2 particles exert strong interface bonding and low crystallographic mismatch with Al–Si matrix.•By optimizing the spatial distribution of TiB2 particles, composites outstanding strength-ductility synergy are achieved.