In-situ LDHs growth on PEO coatings on AZ31 magnesium alloy for active protection: Roles of PEO composition and conversion solution

In this work, plasma electrolytic oxidation (PEO) coatings were produced on magnesium alloy AZ31 in aluminate, silicate and phosphate- based electrolytes, and followed by hydrothermal treatments in order to synthesis layered double hydroxides (LDHs) based nanocontainers. LDHs synthesis was done in three different growth solutions (deionized water, sodium nitrate and aluminum nitrate containing solution). In frame of this work it was shown, that it was difficult to form LDHs on Si-based PEO coating, due to more stable silicate phases in comparison with aluminate and phosphate phases in respective PEO coatings. The obtained hybrid LDH/PEO coatings were characterized using SEM, EDS and GDOES, and then the corrosion protection was further investigated by EIS. Based on the obtained results, it was confirmed that, the hydrothermal treatments in Al3+ containing solution played an important role on overall corrosion resistance for phosphate and silicate-based PEO coatings, but not for Al-based PEO coatings.