Preparation And Properties Of Conversion Coatings On Magnesium Alloy From Deep Eutectic Solvents

Magnesium and its alloys have potential applications in aerospace,electronics,automotive industry and biomedicine owing to their high specific strength,excellent biocompatibility and available recyclability.However,the corrosion resistance of Mg is seen as one of the key ??Achilles heels” of the metal that restricts the usefulness of Mg alloys.The most frequent and reliable strategy for improving the corrosion resistance of Mg alloys is modifying the surface.Conversion film is one of the common surface modification methods,which is produced by chemical or electrochemical treatment on metal surface.However,most conversion films on Mg alloys are prepared from the aqueous solutions,which is difficult to be controlled due to the occurrence of hydrogen evolution.Deep eutectic solvents(DESs)are a new type of ionic liquid with several advantages such as lower toxicity and easy availability,which are suitable for the preparation of conversion films on the surface of magnesium alloys.Therefore,we proposed DES-based conversion films on the magnesium alloy to improve the corrosion resistance of substrates.(1)A hydrophobic epoxy resin coating with a deep eutectic solvent(DES)-based conversion pretreatment was proposed to enhance the corrosion resistance of magnesium alloys.First,a porous conversion film was prepared on the surface of the magnesium alloy by heating method.Then,a hydrophobic epoxy resin coating was dip-coated on the conversion film.It was found that the porous conversion pretreatment was ready to trap more waterborne epoxy resins during the dip-coating process and provide strong bonding interface.Corrosion tests indicated that the corrosion current density of double layered hybrid coating system was decreased by three orders of magnitude,which should be attributed to the hydrophobicity of the surface layer,the dense and adhesive epoxy resin,and the corrosion resistant DES-based conversion pretreatment.(2)Aiming at the application of bio-magnesium alloy materials,lithium chloride-urea deep eutectic solvent conversion film was prepared on the surface of pure magnesium and magnesium alloys by ionothermal method.The type of conversion film had a flower cluster structure on the surface of pure magnesium,while it was more dense on the surface of magnesium alloy with some cracks.Corrosion resistance and in vitro biocompatibility tests were performed in Hank's and PBS solutions.The experimental results showed that the corrosion current density of the conversion film in the simulated body fluid was decreased by two orders of magnitude,the hemolysis rate of the conversion film was less than 5%,and it had the effect of inhibiting the growth of bacteria...