Protective Performance of Plasma-Enhanced Chemical Vapor-Deposited Ethyl Cyclohexane Coating on Magnesium Alloys

In the present investigation, plasma-polymerized ethyl cyclohexane (ECH) coatings were deposited onto AZ31 and AM50 magnesium (Mg) alloys using plasma-enhanced chemical vapor deposition. The influences of deposition time on the coating formation, surface morphology, chemical composition and electrochemical corrosion behavior were investigated. The coating deposition was confirmed by infrared spectroscopy (FT-IR), and the thickness was measured using a scanning electron microscope. Energy-dispersive x-ray analysis revealed an increase in carbon and a decrease in Mg concentrations as the coating duration was increased. Electrochemical impedance spectroscopy (EIS) results confirmed an improvement in the corrosion resistance of AZ31 and AM50 alloys due to ECH coatings in the presence of a 3.5 wt.% NaCl solution. Further, equivalent circuit curve fitting analysis of the EIS results indicated an increase in charge transfer resistance (R_ct) values with longer coating durations. These results confirmed the protecting ability of ECH coatings against corrosive ion attack, which was also substantiated by the surface morphologies after corrosion. Impedance values decreased as the duration of exposure in a NaCl solution increased, and the coating prepared using a 30-min ECH deposition exhibited better protection properties.