In the present study, Mg-Al layered double hydroxide (Mg-Al/LDH) was synthesized on the surface of AZ31 Mg alloy substrate via in-situ hydrothermal treatment. Synthesis parameters were changed to determine their effect on the lateral size of LDH. For this purpose, etching in nitric acid and anodizing in sodium hydroxide solution were performed as surface pretreatments. Moreover, the influence of LDH solution pH (10 and 11) on the lateral size of LDH coating was investigated. Morphology, chemical composition, and crystalline structure were characterized by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), Fourier transform infrared (FTIR) spectroscopy, and X-ray diffraction (XRD). The corrosion resistance of the coatings was investigated by H₂ measurements, salt spray, and electrochemical impedance spectroscopy (EIS). Moreover, the epoxy coating was applied on the best anti-corrosive LDH sample for assessing the compatibility and effectiveness of LDH on the corrosion properties of the substrate with the epoxy layer. At pH = 11, the lateral size of LDH was smaller than samples at pH = 10. In addition, small-sized LDH, as well as LDH/epoxy coating, revealed enhanced corrosion protection.

Polybenzoxazine (PBz) resins exhibit excellent mechanical, thermal, and adhesive properties, making them interesting candidates for coating applications. Moreover, thanks to the incorporation of exchangeable ester bonds within the PBz network, the coating presents healable properties that are catalyzed by the intrinsic presence of tertiary amine within the PBz backbone. Unfortunately, these tertiary amine functions are also responsible for the limited resistance of such systems to acid environments by protonation. To address this limitation, the protection of tertiary amines inherent to the PBz network was investigated in this study by incorporating an aromatic group close to the amine function to minimize its protonation via hindrance/mesomeric effects. More precisely, benzoxazine precursors based on monoethanolamine (mea) and aminophenylethyl alcohol (Apa) were synthesized and tested as protective coatings of aluminium alloy substrates (AA1050). The resins were characterized by NMR, FTIR, rheology, TGA, DSC, and DMA. PBz synthesized from Apa exhibits enhanced thermal stability, reduced swelling rates in both water and acid, and shortened relaxation times. After application via solvent casting on AA1050 substrates, the acid resistance of the coatings was evaluated. Electrochemical impedance spectroscopy results demonstrated better resistance of the Apa-based resins in 0.1 M sulfuric acid after one month of immersion.