Enhancement of corrosion resistance of AZ31 Mg alloys by one-step in situ synthesis of ZnAl-LDH films intercalated with organic anions (ASP, La)

Inserting corrosion inhibitors into a lamellar protective coating is an effective way to improve the corrosion resistance of metal substrates. In this work, two kinds of environmentally friendly organic acid anions, aspartic acid (ASP) and lauric acid (La), were explored as corrosion inhibitors to in situ intercalate into the ZnAl-layered double hydroxides (ZnAl-LDHs) on AZ31 magnesium alloys by a facile one-step hydrothermal method. The morphology, composition, structure and the corrosion resistance of these two LDHs coating before and after corrosion experiment were investigated. It is found that both the two kinds of ZnAl-LDHs films consist of uniform and dense layered nanosheets (NSs), and the NSs of ZnAl-ASP-LDHs films grow vertically, but those of ZnAl-La-LDHs films exhibit a staggered tilted structure. The corrosion current density of the two ZnAl-LDHs films are two orders of magnitude lower than that of Mg alloy substrate. After one week's immersion in NaCl solution, the NSs structure of two kind of ZnAl-LDHs films still remains the uniform and densely coverage on Mg alloy. Owing to the larger d(003) spacing, the ZnAl-La-LDHs have better ability to absorb Cl− and release interlayer anions than ZnAl-ASP-LDHs. These results indicate that the ZnAl-LDHs films intercalated with organic anions, specially La anions, can significantly improve the corrosion resistance of Mg alloy.