A novel integrated stir–ultrasonic–squeeze casting route for fabricating AA6061-based metal matrix hybrid nanocomposites with enhanced tribomechanical properties

Abstract This study introduces a novel integrated stir–ultrasonic–squeeze casting technique for fabricating high-performance aluminium metal matrix hybrid nanocomposites (AMMHNCs) based on AA6061 alloy, reinforced with 3 wt.% boron carbide (B 4 C) and 2 wt.% graphite (Gr) nanoparticles. Existing fabrication methods often suffer from nanoparticle agglomeration, poor dispersion, and high porosity, which compromise mechanical and tribological performance. The proposed approach overcomes these limitations by combining mechanical stirring for initial dispersion, ultrasonic agitation for deagglomeration and uniform distribution, and squeeze casting for densification and improved interfacial bonding. Microstructural analysis confirmed significant grain refinement and homogeneous reinforcement distribution, particularly in the integrated process. The fabricated AMMHNCs exhibited enhanced mechanical properties, achieving a Brinell hardness of 68.61 BHN, ultimate tensile strength of 175.91 MPa, and elongation of 5.09%. Tribological testing revealed the lowest wear rate and coefficient of friction among all compared processes. These improvements are attributed to the synergistic effects of Hall–Petch grain boundary strengthening and Orowan dislocation pinning mechanisms enabled by nanoscale reinforcements and optimised processing. Compared to conventional stir casting, ultrasonic-assisted casting, and other methods, the proposed hybrid technique offers a scalable, cost-effective, and superior route for producing lightweight, wear-resistant nanocomposites for advanced engineering applications.