A Review of Plasma Polymer Coatings in Corrosion Protection of Metallic Materials

This paper reviews recent research results on plasma polymer coatings applied to metal substrates for improved corrosion protection. Low-temperature plasma polymerization is a promising pretreatment technique for metallic materials to create environmentally-friendly coating systems for corrosion protection. The pinhole-free plasma polymer thin coatings, especially those deposited from organosilicon monomers, such as trimethylsilane (TMS), can be used as an interface adhesion promoter to enhance the adhesion of organic coatings to metallic substrates. Recent research results clearly demonstrated that plasma interface engineered coating systems had excellent corrosion protection to various metallic materials including steel and Al alloys. However, knowledge on how the unique physical and chemical properties of the plasma polymer films relate to the corrosion performance of the coated metals is still lacking and is of great interest. Our recent research efforts have been directed towards further understanding the role of these plasma polymerized silane coatings in corrosion protection. The effects of plasma polymer coatings on alclad Al alloy 2024-T3 [2A] and magnesium alloy AZ31B [Mg] have been investigated using electrochemical characterization techniques, including linear polarization, cyclic polarization (CP) and electrochemical impedance spectroscopy (EIS). The experimental results illustrated that, due to their very low thickness, the ultra-thin plasma polymerized silane thin coating alone provided very limited corrosion resistance. The main contribution of these plasma polymer coatings to the excellent corrosion protection of metallic materials was the enhanced water-insensitive interface adhesion, or tenacious wet adhesion, of the resulted plasma interface engineered coating systems.