In-situ incorporation of LDH particles during PEO processing of aluminium alloy AA2024

The preparation and properties of oxide coatings obtained by plasma electrolytic oxidation in close to pH-neutral titanium oxide oxalate K2TiO(C2O4)2 electrolyte on aluminum AA2024 have been investigated and discussed. Immobilization of different Zn-Al layered double hydroxides (LDH) have been tested: LDH[CO3] and LDH[MBT]. LDH[CO3] was also tested with 2-mercaptobenzothiazole (MBT) as an additive to the PEO electrolyte. Obtained coatings are characterized with respect to their morphology, phase and chemical composition, photocatalytic activity and anti-corrosion properties. Obtained PEO coatings show typical PEO morphology, except a particular foamy structure achieved for coatings in LDH[MBT]-containing electrolyte, allowing interesting possible applications, particularly in the field of photocatalysis. All coatings contain elements originating from both the substrate and the electrolyte, with EDS analysis displaying a prominent presence of Ti, and the presence of Zn originating from LDH addition to standard electrolyte. XRD patterns of formed PEO coatings reveal the changing ratio of anatase-to-rutile, but with additional formation of crystalline phases such as K0.12Ti8O16, Ti5O9, Ti2O3, γ-Al2O3 and ZnAl2O4. Despite a standard PEO surface morphology, the highest photocatalytic activity reaching 52 % is observed for coatings created in LDH[CO3]-containing electrolyte. Notable anti-corrosion properties were achieved for coatings with LDH[CO3] and MBT added to the electrolyte.