Corrosion Behavior of B₄C, SiC, and MWCNT-Reinforced Al 7075 Hybrid Metal Matrix Composites in a Simulated Marine Environment

Abstract

Al 7075-based hybrid metal matrix composites reinforced with boron carbide (B₄C), silicon carbide (SiC), and multi-walled carbon nanotubes (MWCNTs) was fabricated by the stir casting route. This paper reports the corrosion behavior of nine composite variants under simulated marine conditions. Immersion corrosion tests were performed on rectangular coupons (20 mm × 20 mm × 5 mm) in 3.5 wt% NaCl solution at room temperature for 24 hours, following the weight-loss procedure of ASTM G31. Corrosion rate was computed from weight loss, exposed surface area, composite density, and exposure time. Corrosion rate decreased monotonically from Run 1 to Run 9, indicating that increasing ceramic reinforcement content (B₄C, SiC) together with MWCNT addition improves resistance to chloride-induced corrosion, most likely through a combination of reduced exposed metallic area, more stable passive-film formation, and reduced micro-galvanic activity at the reinforcement–matrix interface. Benchmarked against unreinforced Al 7075 corrosion rates reported in the peer-reviewed literature (weight-loss method, identical NaCl concentration and temperature), the least-reinforced composite in this study (Run 1) already showed roughly a five-fold reduction in corrosion rate, and the most heavily reinforced composite (Run 9) an approximately six- to seven-fold reduction. These findings support the suitability of B₄C/SiC/MWCNT-reinforced Al 7075 hybrid composites for structural and tribological applications in chloride-rich, marine service environments.