The inhibitive action of some quaternary N-heterocyclic compounds namely 1-methyl-4[4'(-X)-styryl] pyridinium iodides (X: -H, -Cl and -OH)on the corrosion of Al-Cu alloy in 0.5 M HCl solutions was evaluated by potentiodynamic polarization, electrochemical impedance spectroscopy and weight loss measurements. All the studied compounds showed good inhibitive characteristics against the corrosion of Al-Cu alloy in the tested solutions and their performance increases with inhibitor concentration. Polarization data indicated that the studied compounds are cathodic inhibitors without changing the mechanism of hydrogen evolution reaction. The adsorption of all inhibitors on Al-Cu alloy obeys Langmiur adsorption isotherm. The effect of temperature (30-70 degrees C) on the inhibition efficiency at certain concentration of the studied compounds was investigated. The data revealed that the studied compounds have good pickling inhibitor's quality as they perform well even at relatively high temperature. The corrosion activation parameters (E-a, Delta H*, Delta S* and Delta G*) were estimated and discussed. It was found that E values for Al-Cu alloy corrosion in the inhibited solutions were higher than that for the uninhibited solution, indicating good inhibitor characteristics with physical adsorption mechanism. The effect of acid s anion on the performance of the studied inhibitors was studied and discussed. (C) 2008 Elsevier B.V. All rights reserved.