Fracture Surface Morphology and Mechanical Performance of Al7075 Composites Reinforced with B₄C, Gr and ZrO₂ particles

This study investigates the mechanical behaviour and fractographic properties of Al-7075 metal matrix composites that are individually reinforced with 3 weight percent boron carbide (B₄C), graphite (Gr), and zirconia (ZrO₂) using a two-step stir-casting. To assess the impact of specific reinforcements on mechanical response and fracture processes, three composite systems were created, Al7075+B₄C, Al7075+Gr, and Al7075+ZrO₂. Strong interfacial bonding with the aluminium matrix and uniform reinforcement dispersion were verified by microstructural characterization using energy dispersive spectroscopy (EDS) and scanning electron microscopy (SEM). Tensile and hardness tests were used to assess the mechanical behaviour of the composites. Compression- and impact-fractured specimens were then subjected to in-depth fractographic examination to determine the predominant failure mechanisms. The B₄C-reinforced composite exhibited enhanced strength and load-bearing capacity, reflected by brittle cleavage features and reduced plastic deformation. In contrast, the graphite-reinforced composite demonstrated improved toughness, characterized by ductile fracture behaviour with pronounced dimpling and effective crack deflection. The ZrO₂-reinforced composite displayed mixed-mode fracture characteristics, governed by localized plastic deformation and particle–matrix interfacial debonding. The novelty of this work lies in the direct comparative evaluation of mechanical behaviour and fracture surface morphology of Al-7075 composites reinforced with B₄C, Gr, and ZrO₂ at an identical reinforcement content, providing insight into the structure–property relationships of individually reinforced Al-7075 composites.