Design and development of heterogeneous aluminum matrix hybrid composites for enhanced ductility

Traditional aluminum-based composite materials are limited in application due to the contradiction between strength and ductility. To address this, a dual matrix composite system based on Al-TiO₂-H₃BO₃ was developed using ball milling, cold pressing, and sintering. In this system, ball-milled aluminum forms the internal matrix with in-situ reinforcements, while unmilled aluminum, added in proportions from 0 % to 75 %, creates an outer matrix known as the reinforcement-lean zone (RLZ). By introducing un-ball-milled aluminum to form RLZ with scarce reinforcement, the strength and toughness were synergistically optimized. Dual matrix hybrid composites were sintered at temperatures between 600°C and 800°C, following differential thermal analysis that indicated the formation of reinforcing particles above 550°C. X-ray diffraction and Energy Dispersive Spectroscopy confirmed the presence of in situ reinforcements such as γAl₂O₃, AlB₂, TiB₂, and Al₃Ti within the aluminum matrix. Microscopy demonstrated dual matrix morphology displaying rearrangement of the RLZ and reinforcement-rich zone (RRZ). Maximum microhardness and strength were observed at a sintering temperature of 800°C. The composite with 0 % unmilled aluminum exhibited the highest hardness of 169.2 HV, whereas the highest toughness of 6.12 Jm-3 was achieved in the composite containing 75 % unmilled aluminum. Atomic Force Microscopy revealed a progressive decrease in surface roughness from 19.70 nm to 7 nm as the proportion of unmilled aluminum increased from 0 % to 75 %.