Effectiveness of corrosion protection for 6061 aluminum with orchid leaf extract inhibitor in 1M HCl solution

Understanding the corrosion behavior of aluminum in acidic environments requires both experimental and molecular-level investigation. This study investigates the effectiveness of Orchid leaf extract (OLE) as a green corrosion inhibitor for Aluminium alloy 6061 (AA6061) in 1 M HCl solution using combined experimental and computational approaches. Potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS) revealed optimal inhibition efficiencies of 90.11% and 80.07%, respectively, at 3000 mg L⁻ 1 . The adsorption process followed the Langmuir isotherm, with a free energy of adsorption (ΔGₐds = –27.31 kJ mol⁻ 1 ), indicating a synergistic mechanism of physisorption and chemisorption. Phytochemical components containing aromatic rings and oxygen-bearing groups were modeled as representative inhibitor molecules (A₁ and A₂). Density functional theory (DFT) and Monte Carlo simulations confirmed that both molecules can adsorb strongly onto the Al (111) surface through electron donation and charge transfer, showing higher adsorption energies than water molecules. Fourier transform infrared (FT-IR) and UV-Vis spectroscopy verified the interaction of functional groups such as –OH, C=O, and aromatic rings with the aluminum surface. Scanning electron microscopy (SEM) demonstrated that the inhibitor forms a compact protective film, markedly reducing corrosion damage.