Study on the Corrosion Inhibition Performance of Benzothiazolium-Based Ionic Liquids for Aluminum Alloys

3-Ethyl-2-methylbenzothiazolium iodide ([EMBT]I), a benzothiazolium-type ionic liquid, was designed and prepared. Its corrosion-inhibiting performance for aluminum alloy in HCl solution was then evaluated. The inhibition behavior and mechanism of [EMBT]I were systematically investigated using the weight-loss method, electrochemical tests, scanning electron microscopy (SEM), contact angle (CA) measurement, Fourier transform infrared spectroscopy (FTIR), and quantum chemical calculations. Experimental data confirm that [EMBT]I provides strong corrosion protection for aluminum alloy, with a mass-loss inhibition efficiency reaching 98.58% at 10 mmol/L and 308.15 K. Adsorption follows a Langmuir isotherm and is spontaneous and endothermic. The inhibitor acts mainly through cathodic suppression and the formation of a protective film on the alloy surface. Quantum chemical calculations further reveal that the benzene ring, C═C bond, and planar thiazole ring in [EMBT]I are considered the main anchoring sites, while the I- anion exerts a synergistic adsorption effect together with the cationic moiety, thereby effectively retarding the corrosion process. The present investigation furnishes a theoretical groundwork for designing high-performance corrosion inhibitors based on ionic liquids.