Inhibitory effect of cysteine and lanthanides on AA7075-T6 in neutral NaCl solution

The inhibitory effect of cysteine in the presence of selected lanthanide chlorides (LaCl3, NdCl3, and CeCl3) in a neutral 0.1 M NaCl solution was analyzed. The cysteine concentration of 0.3 mM was determined as an optimal one. The resistance to general and pitting corrosion of AA7075-T6 alloy in inhibitive solutions was determined using electrochemical impedance spectroscopy and potentiodynamic polarization measurements. The surface appearance of the aluminum alloy was determined before and after corrosion tests using scanning electron microscopy/energy dispersive spectroscopy, while the presence of an inhibitory layer on the alloy surface was confirmed by X-ray photoelectron spectroscopy analysis and atomic force microscopy. The inhibitory effect of cysteine was significantly higher in the presence of all tested lanthanide chlorides, especially to pitting corrosion. The protective ability of cysteine was increased by lanthanides in the following sequence: Ln < Nd < Ce ions. The inhibitory effect of cysteine in the presence of cerium ions was examined in more detail as cerium ions provided the highest inhibitory effect, both to general and pitting corrosion.