Improved mechanical and tribological behavior of the novel Al–AlMgB14–graphite hybrid nanocomposite via optimized mechanical milling

In this study, a novel Al-5 wt. % AlMgB 14 -1 wt. % graphite hybrid nanocomposite was fabricated through mechanical milling followed by hot pressing. The influence of milling time (0–30 h) on powder characteristics, microstructural evolution, densification behavior, and the resulting mechanical and tribological properties was systematically investigated. X-ray diffraction analysis revealed notable crystallite refinement (from 92.4 to 24 nm) accompanied by increased lattice strain and dislocation density with increasing milling time. The results demonstrated that the sample milled for 25 h exhibited the best overall performance, achieving a microhardness of 173 HV (a 116 % improvement), a yield strength of 450 MPa (a 183 % improvement), and a compressive strength of 556 MPa (a 146 % improvement), representing substantial improvements compared to the unmilled condition. Tribological testing also showed substantial improvements, with the coefficient of friction and wear rate decreasing by approximately 70 % and 85.5 %, respectively. The wear performance improved due to the enhancement of the mechanical properties, the formation of a durable mechanically mixed layer (MML), and the solid lubricating effect of graphite. However, excessive milling (30 h) resulted in particle agglomeration, reduced densification, and a slight deterioration in mechanical properties. The improvements in mechanical performance were mainly attributed to the combined effects of crystallite size reduction, homogeneous reinforcement distribution, strain hardening, and effective load transfer mechanisms. This work demonstrates the critical role of milling time optimization in achieving balanced microstructural refinement and performance enhancement in aluminum hybrid nanocomposites and provides practical insight into processing-structure-property relationships for advanced aluminum matrix nanocomposites.