Preparation And Characterization Of Az31 Magnesium Alloy With Superhydrophobic And High Corrosion Resistance Coating

Magnesium alloys have many advantages such as low density,high specific strength,good damping and good cutting performance.They are widely used in manufacturing fields including new energy vehicles,hydrogen storage devices and medical materials.However,magnesium alloys are positive and prone to corrosion in applications.In this research,a rough surface with micro-nano structure was prepared by chemical deposition and electrodeposition,and a super-hydrophobic coating was obtained under the modification of low surface energy substances,which greatly improved the corrosion resistance of magnesium alloy.The main research results are listed as follows:(1)Super-hydrophobic coatings were obtained by electroless particle reinforced Ni-P-TiO₂composite coatings,electroplating cobalt plating and modification with 1wt.%fluorosilane ethanol solution.The surface morphology of the superhydrophobic coating is a micro-nano composite structure with convex hull-like and villi-like structure.The overall surface roughness of the coating is 554nm,its static contact angle is about 158.2°and the rolling angle is about 3.5°.The optimal addition amount of TiO₂ nanoparticles is 2g/L,and the corrosion resistance of the particle-reinforced Ni-P-TiO₂ composite coating is improved by an order of magnitude compared to the Ni-P alloy coating.The self-corrosion current density of the superhydrophobic coating is 9.1×10^-7 A/cm²,which has improved by two orders of magnitude compared with the corrosion resistance of Ni-P alloy coating.When the friction distance is700 mm,the contact angle of the superhydrophobic coating is 151.5°and it still maintains good hydrophobicity.(2)TiO₂ sol was added to the electroless plating solution instead of adding TiO₂ nanoparticles.The prepared sol-enhanced Ni-P-TiO₂ composite coating has better mechanical properties as the TiO₂particles were more uniformly dispersed in the coating.On the basis of sol-enhanced Ni-P-TiO₂composite coating,the cobalt layer was electroplated.The surface roughness is 547nm.The static contact angle after surface modification is about 157.7°and the rolling angle is about 4.0°.The optimal dosage of TiO₂ sol is 10m L/L,and the corrosion current density of the sol-reinforced composite coating is 2.7×10^-6A/cm².Compared with Ni-P-2g/L TiO₂ composite coating,the corrosion resistance is improved by 38.6%.The self-corrosion current density of the superhydrophobic coating is 6.4×10^-7A/cm².Compared with super-hydrophobic coatings based on Ni-P-2g/L TiO₂ particle coatings,its corrosion resistance is improved by 29.6%.The test results of friction show that the coating has good stability,the contact angle is 150.1°when the friction distance is 800 mm.(3)Single-layer sol reinforced composite coating was replaced by electroless plating of sol-enhanced double-layer Ni-P/Ni-P-10m L/L TiO₂ composite coating.Compared with the single-layer sol-enhanced Ni-P-10m L/L TiO₂ composite coating,its corrosion resistance increased by 56%.Based on the double coating,the super-hydrophobic coating has a surface roughness of 527nm.The contact angle after surface modification is about 156.9°and the rolling angle is about 5°.Its self-corrosion current density is 5.6×10^-7 A/cm²,which is 12.5%higher than the corrosion resistance of the super-hydrophobic coating built on the Ni-P-10m L/L TiO₂ sol coating,indicating a further improvement of corrosion resistance for magnesium alloy.When the friction distance of the superhydrophobic coating is 700mm,the static contact angle drops to 151.1°,indicating a good stability of the coating.