The inhibition effect of amino acids and hydroxy carboxylic acids on pitting corrosion of aluminum alloy 7075

Fitting corrosion of aluminum alloy 7075 in 0.05 M NaCl solution at pH values of 4, 5, 7 and 8 were examined by potentiostatic method. It was found that addition of 10(-2) M hydroxy carboxylic acids or amino acids to NaCl solutions cause shifting of E-pit values to noble directions. Amino acids are more effective in shifting E-pit values to noble directions in acidic solutions while hydroxy carboxylic acids are effective in shifting E-pit values to noble directions in neutral or basic solutions. Additions of 1 x 10(-2) M NaNO3 to NaCl solutions, which contain amino acids or hydroxy carboxylic acids, were also investigated. Using hydroxy carboxylic acids with NaNO3 causes shifting of E-pit values to noble directions. But using amino acids with NaNO3 has no effect on passivation of alloy 7075. It was found that organic inhibitors which are effective on pitting corrosion, can compete with the inhibition effect of CrO42-. (C) 2001 Elsevier Science Ltd. All rights reserved.