Mitigating Magnesium Reactivity in CeO2-Containing Waterborne Coatings Through ZrCC and LDH Surface Pre-Treatments

Organic coatings are used as one of the most effective strategies for the corrosion protection of metals. Nowadays, due to environmental regulations, the use of water-based coatings has become essential compared to solvent-based ones. However, their application to magnesium alloys remains largely unexplored due to their high reactivity with water. In the present work, a phosphate-functionalized waterborne binder is applied to AZ31B magnesium alloy. The surface has been modified by four different pre-treatments, respectively: (i) mechanical grinding, (ii) pickling, (iii) conventional conversion treatment, and (iv) a novel conversion treatment based on layered double hydroxides (LDH). The most promising pre-treatments are selected to explore their synergy with a biobased waterborne binder, containing CeO2 nanoparticles as a corrosion inhibitor. The morphology and composition of the different systems are studied, prior to and after corrosion tests in NaCl solution, by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). Results obtained by electrochemical impedance spectroscopy (EIS) in NaCl solution have revealed not only that LDH performs better than the conventional conversion treatment but also the synergy between LDH pre-treatment and CeO2 nanoparticles when two organic layers are used.