Preparation And Performance Research Of Micro-Nano Structures On 5052 Al Alloy Surface

A lot of progress in science and technology comes from the natural world.It is the source of intellectual thought and inventiveness to imitate special structures and functions of biological surfaces.Inspired by biological features,the preparation of micro-nano structures has become an interdisciplinary research hotspot.It can also render materials and parts some new functions by changing the interfacial interactions.Hence,it is getting a lot of attentions by the worldwide researchers.At present,the preparation of micro-nano structures is found with some problems of poor controllability,complex operation,low preparation efficiency,expensive equipments and simple structures.Meanwhile,few works have been done about the theoretical design and controllable preparation of micro-nano structures.Al alloys,as typical engineering materials,have been widely applied in aerospace,vessel,automotive,architecture and power industries.However,their self-cleaning,anti-corrosion and anti-ice behaviors concerning the interfacial properties are urgent engineering problems in above application fields.Hence,this paper focuses on 5052 Al alloy by investigating preparation methods and performance characteristics of composite micro-nano structures to reveal the effect of interfacial features on superhydrophobic and anti-corrosion behaviors.On account of the composite micro-nano structures on superhydrophobic surfaces,the theoretical design and controllable preparation of primary convex structures are conducted on the basis of studying wetting parameters of secondary structures.The findings are as follows:(1)Two-step etching and etch-electrodepositing methods are adopted to prepare composite micro-nano structures on Al alloys surfaces.Meanwhile,the effect of processing parameters on structural morphologies and dimensions is also discussed.Results show that the micronano structures with two-stage features are firstly achieved by an etching process in hydrochloric acid(6 min)and then respectively boiling(300s)and depositing(60 s,-0.5 V,30 mM silver nitrate solution)processes.The resultant primary structures are multilayer terrace-like structures with edge dimensions of 1-5 ?m.And the secondary structures are pores with sizes of about 200 nm and Ag dendrites,respectively.(2)Based on the theory of surface wettability,the static and dynamic wetting behaviors of various micro-nano structures are investigated to reveal the interactive mechanisms among composite structures,interfacial properties and superhydrophobicities.Results show that composite characteristics can increase the surface roughness,reduce the viscous resistance of liquid and improve the retention of air,which exhibits the solid-gas-liquid interfacial characteristics in Cassie state.Through the further calculation,the liquid-air contacting fractions of composite structures prepared by two-step etching and etch-electrodepositing methods are as high as 86.9% and 89.9%,respectively.Both methods are higher than the critical value of 83.5% for a superhydrophobic surface.Under this condition,it can achieve less energy barrier that water needs to overcome and also obvious superhydrophobic effect.(3)Anti-corrosion behaviors on surfaces with different micro-nano structures are tested by the potentiodynamic polarization and impedance spectroscopy technologies.In view of the equivalent circuit models,the characterization of corrosion parameters and quantitative description of interfacial behaviors are conducted to investigate the effect of superhydrophobic composite interfaces on corrosion resistances.Results show that before 20 days of immersion,the anti-corrosion mechanism of composite micro-nano structures in Cassie state is found with the physical isolation of superhydrophobic membrane layer and its driving effect.Thus its corrosion resistance is superior to other single preparations.With the extension of immersion time,the corrosive medium permeates superhydrophobic films gradually.And then the substrate/film interfaces are destroyed.After 40 days,the damage of superhydrophobic films on the two-step etching sample has lost the protective effect of metal substrates.Hence,its corrosion resistance is close to the polishing sample.While for the etch-electrodepositing sample,dissimilar metal deposition directly leads to the galvanic corrosion suggesting a lower corrosion resistance than the polishing sample.(4)On account of the composite micro-nano features on superhydrophobic surfaces,the theoretical design of rimary convex structures are conducted on the basis of studying wetting parameters of secondary structures.Based on the spherical feature of a droplet under the minimum energy principle,the interfacial meniscus feature between convex structures is defined.Besides,the prediction model of static liquid contact angles on composite convex structures is established by calculating the liquid-air contacting area.Based on the balance equation of suspended droplets on convex structures,the dimension design criterion of ordered micro-convex structures is deduced under Cassie state.Using common WEDM,the theoretical design and controllable preparation of primary convex structures are achieved by considering the prediction model of contact angles and dimension design criterion of Cassie state.Meanwhile,the rationality of the theoretical design criterion is also proved.