Study On Fabrication,Anti-corrosion And Antifouling Performance Of Superhydrophobic Aluminum Alloy Surface

Aluminum is one of the most widely used metals in the field of nonferrous metals.Aluminum and its alloy has good physical and chemical properties,widely used in many fields which has the characteristics of good appearance,light weight,ductility and good mechanical processing.However,aluminum alloy can be easily corroded in acid,alkali,and some wet or salty environment.Additionally,the surface of aluminum alloy can be easily polluted under the atmospheric environment or some special conditions.All of these can hinder the practical application of aluminum and its alloy in various degrees.Inspired by the“lotus leaf effect’’,the superhydrophobic surface with contact angle larger than 150°has exhibited excellent corrosion resistance,antifouling and self-cleaning performance.Therefore,it is very important to explore a simple and effective method to construct the superhydrophobicity on the aluminum alloy surface in order to improve the corrosion resistance,self-cleaning,and antifouling properties.In this work,we put forward without pre-polishing technique,a facile and environment-friendly method is developed to fabricate the superhydrophobic aluminum alloy surface via boiling water treatment and stearic acid immersion in alcohol-water solution.Meanwhile,simple process,saving time,simple equipment,and environmental protection,a low cost is used in this fabrication technique.The superhydrophobic aluminum alloy surface exhibits hydrophobicity,universality,diversity,good stability,and has excellent antifouling and corrosion resistance.In this dissertation,we put forward without pre-polishing technique,the superhydrophobic aluminum alloy surfaces are developed successfully through a facile and feasible two-step method namely,boiling water treatment+Ethanol-Stearic Acid（STA）-H₂O immersion or one-step method,Ethanol-STA-H₂O immersion.The microstructure,chemical structure,corrosion resistance,and self-cleaning performance of the as-prepared superhydrophobic surfaces are studied thoroughly,and the main contents and results are as follows:Fabrication of the superhydrophobic aluminum alloy surface with two-step method:Without pre-polishing technique,the superhydrophobic aluminum alloy surface with a contact angle of 153.8°and a sliding angle of less than 5°is fabricated successfully by a low-cost and environment-friendly two-step method.The effects of boiling water treatment time,Ethanol-H₂O volume ratio,and STA modification time on the surface microstructure and wettability of the superhydrophobic aluminum alloy surfaces are investigated,and the optimum technological conditions are finally determined as follows:boiling water treatment time for 5 min,Ethanol-H₂O ratio of 1:1,and STA modification time for 50 h,50°C.Results show that the surface of aluminum alloy was relatively smooth with the prolongation of boiling water treatment time,the low volume ratio of Ethanol-H₂O and the increasing of the STA modification time.The morphology gradually turned into a"rough worm structure"shape,surface while the contact angle gradually increased.However,after increasing the boiling water treatment time,reducing the Ethanol-H₂O volume ratio and increasing the STA modification time,the contact angle decreased continuously,and the surface morphology of the petal like homogeneous structure of a large number of micro-nano pores gradually became"disorganized".It was concluded that the best superhydrophobicity could be obtained when boiling water treatment time was 5 min,Ethanol-H₂O volume ratio was 1:1 and STA modification time was 50 h and the aluminum alloy surface had a large number of micro-and nano-pore petals and low surface energy material.Preparation of the superhydrophobic aluminum alloy surface with one-step method:Without pre-polishing technique the superhydrophobicity of aluminum alloy surface is successfully endowed by one-step method,and the effects of Ethanol-H₂O volume ratio,and STA modification time on the surface microstructure and wettability of the superhydrophobic aluminum alloy surfaces are explored.Results show that the superhydrophobic film with a water contact angle of 153.6°and sliding angle less than 5°can be achieved when the volume ratio of Ethanol-H₂O,and the STA modification time is 2:1,and 60 h,60°C respectively.Because of the large numbers of micro-and nano-hole structure forms on aluminum alloy surface,while the long alkyl chains with low surface free energy graft on its surface.Consequently,great amounts of air are captured in the hole,and water droplets cannot penetrate into it and can only contact with the surface protuberances.Furthermore,even the slight disturbance can lead to the water droplets roll off the surface.So the aluminum alloy surface obtains the excellent superhydrophobicity.Corrosion resistance of the superhydrophobic aluminum alloy:The corrosion resistance of the superhydrophobic aluminum alloy is investigated by the electrochemical test.Electrochemical measurements show that the corrosion potential of the superhydrophobic aluminum alloy surfaces positively increases and the corrosion current density significantly decreases as compared to that of the blank ones.All of these results indicate that surface superhydrophobicity can significantly improve the corrosion resistance of aluminum alloys,and which is due to the superhydrophobic coating can effectively capture large amounts of air at the interfaces and prevent the corrosive Cl^-dissolved in water from directly contacting with aluminum alloy surface.Thus the anti-corrosion property of aluminum alloy is improved.Self-cleaning and antifouling behavior of the superhydrophobic aluminum alloy surface:The self-cleaning performance is examined with following methods.a)Using the carbon powder,as the simulating pollutants,the ability of water droplets rolling and taking away pollutants on the blank and superhydrophobic aluminum alloy surfaces is examined.b)The untreated aluminum alloys were immersed into the muddy water.By contrast,the superhydrophobic aluminum alloy was immersed into the muddy water and still maintained it’s clean surface without any contaminants.This is due to the low free energy and micro/nanostructures of the surface,and the adhesion between the clay and the surface is very weak.Thereupon,the sample regains it’s original phase,cleanliness after removing it from the contaminants,indicating an outstanding antifouling ability of the surface.This suggests that the superhydrophobic aluminum alloy surface has excellent antifouling and self-cleaning performance.