Metallic Protective Coatings of Magnesium Metal in Ionic Liquids

    Magnesium is a reactive element, poor corrosion resistance and highly unstable, which have limited its industrial applications.One of the most effective ways to improve the corrosion resistance of Mg and its alloys is to form a coating on the surface to isolate them from the environment.This can be achieved by forming or applying some type of functional barrier layer. There are several surface coating treatment techniques,including electrochemical plating (electroplating), conversion coating,anodizing, hybrid coatings, and vapor-phase process. In present work, conversion coatings and electroplating on pure magnesium metal have successfully achieved by using three ionic liquid;hydrate ammonium alum/urea, hydrate aluminum nitrate/urea and aluminum chloride/urea ILs were used to form corrosion protection conversion coating layers on the surface of pure Mg metal. The process was performed at room temperature by immersing Mg metal in each ionic liquid for 40 min. Metal electroplating was applied to magnesium metal and consequently aluminum metal was successfully deposited on uncoated and prior conversion coated magnesium metal from AlCl /urea ionic liquid. The conversion-coated layers were acted as initial preparation for Al deposit and to promote plating.The surface morphology of conversion and electrodeposited layers were examined by Scanning Electron Microscope (SEM), cross-sectional SEM and Atomic Force Microscopy (AFM) whilst the chemical compositions were inspected with Energy Dispersive X-ray analysis (EDXA) and X-ray diffraction (XRD).   The corrosion behavior has been evaluated by galvanostatic polarization experiments in 3.5 wt% NaCl aqueous solution.The three conversion coating layers were homogenous uniform and covered the whole substrate with a nanoscale particle size, roughness, and average height. They were well adhered to the substrate with reasonable allocation, while the average thickness were about (2-5) µm. The EDXA and XRD results showed that aluminum oxide and mixed metal oxides(MgAlxO) complex have been presented in the three conversion coating layers formed on the Mg metal surface.The Al deposited layers on uncoated and conversion coated Mg metal were gray compact and rather rough metallic coating with about (30-50)µm thickness. The corrosion resistance of pure Mg metal was improved by the conversion coating established from the three ionic liquids and the Al electrodeposited layers from aluminum chloride/urea IL. The corrosion potential was shifted to more positive values and the corrosion current has significantly lower value compared to uncoated Mg metal.