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 valu es of 4, 5, 7 and 8 were examined by potentiostatic method. It was found th at addition of 10(-2) M hydroxy carboxylic acids or amino acids to NaCl sol utions cause shifting of E-pit values to noble directions. Amino acids are more effective in shifting E-pit values to noble directions in acidic solut ions 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 acid s or hydroxy carboxylic acids, were also investigated. Using hydroxy carbox ylic 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 corro sion, can compete with the inhibition effect of CrO42-. (C) 2001 Elsevier S cience Ltd. All rights reserved.