Amino Acid Interleaved Layered Double Hydroxides as Promising Hybrid Materials for AA2024 Corrosion Inhibition

Various -amino acid (AA) molecules were screened for their ability to retard the corrosion of AA2024 aluminum alloy substrate. The AAs screened were L-arginine (L-Arg), L-asparagine (L-Asn), L-cysteine (L-Cys), L-cystine, L-histidine (L-His), L-methionine (L-Met), L-phenylalanine (L-Phe), L-serine (L-ser), L-tryptophan (L-Trp), and L-tyrosine (L-Tyr). From their performances compared with that of the reference additives chromate and 2-mercaptobenzothiazolate (MBT), L-Cys and L-Phe were selected, and their layered double hydroxide (LDH) interleaved derivatives were further scrutinized. Different LDH phases, namely, LiAl2, Mg2Al, MgZnAl, and Zn2Al, were tested as hosts for the inhibitor AA substances, and the materials were characterized by XRD, FTIR spectroscopy, and SEM. The efficiencies and durable performances of the hybrid materials as an anticorrosion agents for aluminum alloy 2024 (AA2024) were demonstrated through direct current (DC) polarization measurements, and the evolution of the polarization resistance was recorded. The mechanism of inhibition focused on the most promising hybrid material LDH/L-Cys and was tentatively explained as anion exchange and dissolution of the inorganic framework at the cathodic and anodic corrosion zones, respectively, with the particular occurrence of Cu-rich intermetallic zones. The obtained results evidence that the LDH/L-CYS assembly embedded in the polymer coating retards the corrosion process of the AA2024 substrate after a prolonged immersion time.