In alignment with green chemistry principles, this study evaluates the corrosion inhibition performance of leaf (MELE) and flower (MEFE) extracts of Mussaenda erythrophylla on silicon-aluminum alloy in 0.5 M HCl. A multidimensional approach integrating gravimetric and electrochemical techniques, gas chromatography-mass spectrometry (GC-MS), scanning electron microscopy (SEM), and density functional theory (DFT) at the B3LYP/6-311G level was employed to investigate both the macroscopic inhibition behavior and the underlying molecular mechanisms. Both extracts significantly mitigated aluminum alloy corrosion in the aggressive acidic medium, achieving inhibition efficiencies of 86.78% (MELE) and 84.75% (MEFE) at 0.35 g？L？1. Inhibition was governed by adsorption onto anodic and cathodic sites, consistent with the Langmuir modified adsorption isotherm. SEM analysis revealed a marked reduction in pitting corrosion, confirming the protective role of the adsorbed organic film. GC-MS profiling identified the predominant constituents in each extract: di-n-octyl phthalate and 4,8,12-tetradecatrien-1-ol, 5,9,13-trimethyl in MELE, and phenol, 2,6-bis(1,1-dimethylethyl) in MEFE. Global reactivity descriptors (EHOMO, ELUMO, ΔE, electronegativity χ, hardness η, softness σ, electrophilicity index ω, and fraction of electrons transferred ΔN) revealed strong electron-donating and electron-accepting capacities, along with favorable adsorption energetics.
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