Mitigating Pitting Corrosion in LM24 Aluminium Using Alumina-Engineered Graphene Oxide

Ultrasonic-assisted casting enables dispersion of graphene oxide (GO) in aluminium alloys and can enhance hardness and strength at low reinforcement fractions; however, chloride exposure often triggers localized corrosion near reinforcement-rich heterogeneities and degrades surface mechanical integrity. This study evaluates an interfacial-engineering strategy intended to suppress interface-driven pitting while preserving dispersion benefits. LM24-based nanocomposites containing GO and alumina-interlayer-coated GO (Al\(_2\)O\(_3\)@GO) at identical loadings were fabricated by ultrasonic gravitational stir casting under controlled processing conditions. Dispersion and interface condition were examined by SEM and EDS line scans, followed by corrosion characterization using both immersion mass-loss tests in 3.5% NaCl (24–72 h) and electrochemical measurements (open-circuit potential, potentiodynamic polarization, and electrochemical impedance spectroscopy). Localized damage was quantified through pit-statistics analysis (pit density, areal damage fraction, and size distribution), and the mechanical consequence of corrosion was captured using Vickers microhardness mapping and a hardness-retention index. Relative to uncoated GO composites, the Al\(_2\)O\(_3\)@GO system is expected to exhibit reduced corrosion current density, increased polarization resistance, and a more stable low-frequency impedance response, consistent with a less defective interfacial/passive film and suppressed pit initiation and growth. A first-order correlation between hardness retention and pit damage fraction is introduced to provide a compact screening metric linking electrochemical performance to surface mechanical degradation. The integrated methodology offers a transferable framework for designing and qualifying Al/graphene-family cast nanocomposites for chloride-rich service environments.