Nano-Dispersed Boron Carbide Reinforced Aluminium Metal Matrix Nanocomposites: Fabrication via Ultrasonic Cavitation-Assisted Casting and Investigation of Microstructural, Mechanical, and Wear Properties

Abstract

Aluminium metal matrix nanocomposites (AMNCs) reinforced with nano-scale boron carbide (B4C) particles offer an attractive combination of low density, high specific strength, and superior wear resistance for automotive, aerospace, and structural applications. In this work, nano-B4C particles (average size ~50 nm) were synthesised by high-energy planetary ball milling of commercially available micron-sized B4C powder (0.8 micron) for up to 20 hours under an argon atmosphere. The nano-B4C particles were incorporated into an AA6061 aluminium alloy matrix at volume fractions of 0-2.5 vol.% using an ultrasonic cavitation-assisted casting route operating at 2 kW and 20 kHz. Microstructural characterisation using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), and energy dispersive spectroscopy (EDS) confirmed a fine, largely uniform dispersion of B4C particles within the aluminium matrix together with an elevated dislocation density at the particle-matrix interface. Mechanical characterisation (Vickers/Brinell hardness, uniaxial tensile testing, IZOD impact testing) and dry sliding wear testing (pin-on-disc) revealed that hardness and tensile strength increased progressively with B4C content up to approximately 2.0 vol.%, beyond which particle agglomeration and micro-porosity degraded properties. Elongation to fracture decreased monotonically with reinforcement content, while nano-reinforced composites consistently outperformed micron-reinforced counterparts in wear resistance and impact toughness at equivalent nominal reinforcement content. These findings support ultrasonic cavitation-assisted casting as a scalable, cost-effective route for producing nano-B4C/AA6061 composites with tailored mechanical and tribological performance for structural lightweighting applications.