Hybrid reinforcement of micro-B4C and nano-h-BN in AA6061 aluminum matrix composites: Fabrication, microstructural evolution, and performance mechanisms

We fabricated AA6061 composites reinforced with micro-sized B 4 C and nano-sized h-BN via friction stir processing (FSP), systematically investigating how particle size and hybridization affect microstructure, mechanical properties, and wear performance. The micro-nano hybrid system (M-N) achieved the finest grain refinement down to 0.7 μm through particle-stimulated nucleation (PSN) mechanisms. Strengthening analysis revealed grain refinement as the dominant mechanism, contributing 73.54 MPa to the total tensile strength of 244 MPa. The M-N specimen exhibited exceptional wear resistance (1.11×10 -6 mm 3 (N·m) -1 ), representing a 99% improvement over the matrix. The synergistic effect was attributed to micro-sized B 4 C providing load-bearing capacity while nano-sized h-BN formed lubricating layers, thereby creating an effective protective mechanism. This approach provides a viable strategy for performance optimization in high-volume-fraction particle-reinforced aluminum composites.