| As the lightest metal materials for engineering structure,magnesium(Mg)alloys have the advantages of high specific strength,high specific stiffness,good damping and strong electromagnetic shielding ability,which promises a huge application prospect,such as aerospace,automotive industries,and electronic products.However,Mg alloys are easily corroded due to the inherent high corrosion rate of Mg and their porous oxide/hydroxide films.Poor corrosion resistance is one of the bottlenecks that limit the large-area application of Mg alloys.The surface treatment is an important way to solve the corrosion problem.The biomimetic superhydrophobic surface provides a wise strategy for solving the corrosion of Mg alloys due to its special wettability.The superhydrophobic surface can be used in other fields,such as self-cleaning,anti-icing,anti-bacterial,anti-fouling,oil-water separation,and micro-droplet transportation.With the development of surface technology,some progress has been made in durable,fluorine-free,multifunctional superhydrophobic surfaces or biomimetic surfaces with controllable wettability.Focusing on the corrosion protection of Mg alloys and based on the research progress of biomimetic surface,this paper aims at improving the corrosion resistance of Mg alloys and expanding the surface function of Mg alloys by controlling surface wettability via designing surface composition and micro/nanostructure.A superhydrophobic surface is prepared by laser processing and heat treatment,and the corrosion behavior and anti-corrosion mechanism are investigated.High and low adhesive superhydrophobic surfaces are prepared on Mg alloys by combining chemical etching and chemical modification,and the formation mechanism of high and low adhesive superhydrophobic surfaces,the anticorrosion behavior and mechanism of low adhesion superhydrophobic surfaces are investigated.An electrothermal/superhydrophobic coating for anti-icing and anti-corrosion is constructed using the brushing,scraping and spraying method.The mechanical,chemical stability,electrothermal-healing ability,anti-icing performance and anti-corrosion behavior are investigated.A switchable surface between the superhydrophobic surface(SHS)and slippery liquid-infused porous surface(SLIPS)is obtained by combining brush and laser processing.The wettability transformation behavior is explored,and anti-corrosion behavior and mechanism of the two surfaces are investigated;the advantages and disadvantages of the two surface states in dealing with dynamic droplets are investigated.The main contents and conclusions of the above study are generalized as follows:(1)Superhydrophobic surface is prepared on a Mg-9Al-1Zn(AZ91)Mg alloy sheet via the combination of laser ablation and heat treatment.A wavy surface morphology,similar to mountains and valleys,is written on AZ91 alloy after laser ablation,and the laser-structured surface is superhydrophilic.Simultaneously,the Mg17Al12 phase re-dissolves in the Mg matrix,forming a Al-rich melted layer.The laser-ablated superhydrophilic sample wrapped filter paper is heat-treated at 160 ? for 60 min,transforming into a superhydrophobic surface with a water contact angle(WCA)as high as 158.8±2 °.The transformation of wettability is mainly related to that heat treatment promotes the absorption of organic matter by the laser-ablated structure.The corrosion current density(Icorr)of superhydrophilic AZ91 alloy(33.9 ?A/cm2)is nearly one-quarter of bare AZ91 alloy(147.9 ?A/cm2),and the Icorr of superhydrophobic AZ91 alloy(6.7 ?A/cm2)is more than 1 order magnitude lower than that of bare AZ91 alloy.The results of the immersion experiment show that the synergistic effect of the air layer and Al-rich melted layer improves the corrosion resistance.This study puts forward a new idea for improving the corrosion resistance of Mg alloys by modifying the microstructure in the alloy's near-surface region and surface wettability.(2)Through a simple chemical etching and surface modification,superhydrophobic surfaces with tunable water adhesion are prepared on Mg-3Al-1Zn(AZ31)and AZ91 alloy sheets.The different water adhesions are described by three different wetting model,i.e.Wenzel,Cassie impregnating,and Cassie model.The corrosion current density(Icorr)of low adhesive superhydrophobic AZ31 and AZ91 alloys is about 1 order magnitude lower than that of bare AZ31 and AZ91 alloys,respectively.Immersion test reveals that low adhesive superhydrophobic AZ91 alloy with dense surface microstructure can effectively improve the stability of air layer,exhibiting durable corrosion resistance.Simultaneously,the superhydrophobic surfaces with tunable water adhesion are demonstrated to be feasible in the application of low-loss transport of microdroplet.In addition,the as-fabricated superhydrophobic surfaces show high-temperature stability(180 ? in air for 5 h,90 ? in hot water for 30 min)and chemical stability(WCA(29)150 °,p H=3-13).(3)Herein,through the brushing,scraping and spraying method,we prepare a non-fluorinated electrothermal/superhydrophobic coating on Mg-3Al-1Zn-1Sn(AZT311)alloy.The WCA can reach 166.2±0.8°.The superhydrophobic coating consists of three components,including insulation,electrothermal,and superhydrophobic films.The superhydrophobic coating has an outstanding electric heating capability.When supplying a voltage of 26 V,the saturation temperature of the coating(5 cm×5 cm)can reach about 180 ? under an ambient temperature of-30 ?.The superhydrophobic coating exhibits good mechanical robustness,chemical stability,and in-situ electrothermal-healing ability against plasma and chemical etchings.The superhydrophobic coating with electrothermal characteristics has active de-icing,de-frosting,and anti-icing performance.In an ambient temperature of-30 ? and a simulated high humidity environment,when the surface temperature is increased from-30 ? to-5 ? by electric heating,the number of water droplets bouncing off the coating grows from 0 to greater than 150.In an ambient environment of-30 ?,when an input voltage of 28 V is applied,the ice and frost is fully melted at 52 and 8 s,respectively.(4)Interestingly,the superhydrophobic coating exhibits a long-term anti-corrosion performance.The Icorr of superhydrophobic coating(2.9±10-9 A cm-2)is about 5 orders lower than Icorr of bare Mg alloy(1.68±10-4 A cm-2).After immersion for 14 days,the Icorr of the superhydrophobic coating is 4.3±10-8 A cm-2,exhibiting excellent corrosion resistance.The excellent corrosion resistance results from a dual anti-corrosion effect,that is,a durable air layer(12 days)and excellent resistance of the coating.Besides,the unique in-situ electrothermal-healing ability can in situ recover the coating's corrosion resistance by repairing superhydrophobicity.The Icorr of plasma-etched coating and the electrothermal-healed coating is 5.6±10-8 A cm-2 and 3.1±10-9 A cm-2,respectively.We expect that this research provides a wise strategy for designing superhydrophobic coating with good mechanical robustness,good chemical stability,in-situ self-healing ability,outstanding anti-icing ability,and long-term corrosion protection ability.(5)A switchable surface between the superhydrophobic surface and SLIPS is achieved on AZT311 alloy.Then,the surface can be easily switched between the SHS and SLIPS by alcohol washing and lubricant-infusion.Notably,the switchable surface exhibits an excellent anti-corrosion ability(with large impedance modulus at 10-2 Hz about 1011 ? cm(2)in both surface states.The anti-corrosion abilities of the two surfaces do not have any degradation after being immersed in 3.5 wt.% Na Cl aqueous solution for 60 days.The excellent corrosion resistance is attributed to that the superhydrophobic surface and SLIPS not only have the excellent underlying polydimethylsiloxane(PDMS)@Al2O3+Fe2O3 coating as a barrier,but also has durable air and lubricant layers as a corrosion barrier(60 days),respectively.The superhydrophobic surface and SLIPS can inhibit corrosion at the defect area through non-wetting ability and flowing of lubricant,respectively.The lubricant layer is more stable than the air layer,and the healing ability of the SLIPS can better inhibit corrosion at the defect area than the non-wetting ability of the superhydrophobic surface.The superhydrophobic surface has better droplet transportability,water shielding ability,and self-cleaning ability than those of the SLIPS in dealing with dynamic droplets. |
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