Synergistic Role of PMMA and Ceria-Based Organic-Inorganic Hybrid Coating Mitigating Saltwater Corrosion of Mg-Y-Zn-Zr alloy

Abstract

Magnesium alloys are promising for engineering applications due to their excellent stiffness and mechanical properties. Unfortunately, the low corrosion resistance of Mg alloy in saltwater restricts their widespread use. In the present work, an organic-inorganic hybrid coating comprising PMMA and Ce-salt is synthesized through a sol-gel route to provide an excellent protective barrier against corrosion in 0.1 M NaCl solution. In particular, the CeO2/Ce2O3 particles were embedded in the PMMA matrix, forming a duplex coating wherein Ce-salt behaves as a self-healing and environmental-friendly species providing efficient anti-corrosive shielding. The organic-inorganic hybrid coating was applied in two different ways, i.e., as a polymeric coating of Ce-salts and PMMA (Ce+PMMA) and as layer-by-layer coating comprising of CePT/CeCC and PMMA (CeCC→PMMA and CePT→PMMA.) The coating offered by Ce+PMMA on WZ44 alloy appeared transparent, having micro-cracks. On the contrary, the layer-by-layer coating comprising PMMA on the CeCC (cerium conversion coating) or CePT (phosphate post-treated CeCC) on WZ44 alloys exhibited that the CePT→PMMA possess a porous coating, whereas the CeCC→PMMA barely showed the presence of cracks. The coating thickness of the specimens was around ~ 26 µm with minimal surface roughness (~1.54 µm). The synergistic role of organic-inorganic hybrid coating was evaluated in 0.1 M NaCl solution at ambient condition by potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS). It was observed that entire coated specimens offered improved corrosion resistance than the uncoated specimen. Among all the coated specimens, the CeCC→PMMA specimen exhibited superior corrosion resistance giving a corrosion inhibition efficiency of ~99 %. The long-time EIS study of CeCC→PMMA specimen in 0.1 M NaCl solution at 1h interval demonstrates an increase in the capacitive loop diameter up to 4 h duration, indicating superior corrosion resistance.