Inhibition of Aluminium Alloy AA2024-T3 pitting corrosion by copper complexing compounds

A scanning vibrating electrode technique (SVET) is used to quantify the influence of a range of copper complexing/precipitating reagents on the kinetics of pitting corrosion affecting AA2024-T3 immersed in 5% aqueous sodium chloride (NaCl). It is shown that organic anions such as 2,5 dimercapto, 1,3,4 thiadiazolate (DMTD), benzotriazolate (BTA) and N,N- diethyl, dithiocarbamate (DEDTC), and inorganic ions such as ferrocyanide effectively inhibit pitting corrosion by film formation on Cu rich intermetallic particles (IMPs) and/or precipitation of aqueous copper cations. Inhibitor efficiency increases in the order ferrocyanide < BTA < DEDTC ≈ DMDT. In contrast, the presence of ethylenediamminetetraacetic acid (EDTA) is shown to prevent copper (Cu) replating, but does not lead to any decrease in localised corrosion currents. This supports the idea that that ample cathodic activity can be maintained on Cu-rich IMPs in the absence of any copper replating to sustain stable pitting on AA2024.