Corrosion resistance of Mg-Al LDHs film on magnesium alloy surface by chelating agent-assisted method

In order to reduce the energy consumption of the reaction, the magnesium alloy samples were immersed directly into three conversion solutions and reacted for 9 hours at 60 degree celsius and pH=12. 0 used the chelating agent-assisted method by adding three chelating agents, ethylenediaminetetraacetic acid tetrasodium (EDTA-4Na), sodium citrate (SC) and potassium sodium tartrate (PST) to aluminum nitrate (Al (NO3)(3)) solution, and Mg-Al layered double hydroxides (LDHs) films doped with different chelating agents can be prepared on the surface of magnesium alloys. The microstructure, phase composition, and corrosion resistance of each LDHs film were analyzed by SEM, XRD, FT-IR, etc . The results show that the chelating agent-assisted method can successfully prepare LDHs films with typical layered structure on the surface of magnesium alloys under normal pressure and 60 degree celsius environment ; and three kinds of Mg-Al LDHs films obtained can effectively improve the corrosion resistance of magnesium alloys. Then, by comparing the structural properties of three different LDHs film layers, it is found that the Mg-Al-PST LDHs film prepared by adding PST has the highest density and the largest thickness, reaching up to 1. 4 mu m. The improvement effect of three coatings on the corrosion resistance of magnesium alloys is as follows : Mg-Al-PST LDHs>Mg-Al-SC LDHs>Mg-Al-EDTA LDHs ; The magnesium alloy covered with the Mg-Al-PST LDHs film compared to the blank magnesium alloy, the corrosion current density decreases by about two orders of magnitude, and the total corrosion resistance increases by about one order of magnitude. And based on the analysis of the structure and properties of the obtained LDHs films, it can be seen that the chelating agent-assisted method can prepare Mg-Al LDHs films with better corrosion resistance in-situ on the surface of magnesium alloys under the lower energy consumption condition. The reason may be that the carboxyl group in the chelating agent can accelerate the deposition of Al 3+ on the magnesium substrate and promote the substitution of some Mg 2+ in Mg (OH)2 by Al (3+) to form LDHs.