Corrosion Behavior And Mechanism Of Typical Metal Materials Used In Grid Equipment Under Thin Electrolyte Layer And Alternate/direct Electric Field

With the vigorous development of economy in China,the demand for electricity in entire society continues to grow,which also promotes the construction and development of the national power industry.The enhancement in transmission capacity,the increase in the number of ultra-high transmission lines above 500 k V,and the conversion of single / dual circuit single base towers increase the consumption of metal materials.Aluminum alloys are used in the preparation of grid tower and high-speed rail,since their good processing and plasticity properties,high strength,excellent corrosion resistance as well as good oxidation resistance.In addition,steel is also used in the construction of towers and transmission lines.Considering the poor corrosion resistance of bare steel,galvanized steel is often used in power grid construction to increase the service life of steel.Not only the natural environment such as wind,sun and rain,but the ultra-high voltage electric field existing in the service environment exacerbate the failure of the metal material,resulting in many social problems and economic losses.Therefore,it is urgent to study the corrosion behavior of aluminum alloy and galvanized steel in electric field to ensure the long-term safe operation of these typical materials.In the current work,aluminum alloy A6082-T6,galvanized steel and No.20 carbon steel are selected as the research objects,and our aim is to investigate the corrosion behavior of these typical materials in simulated atmospheric environment with/without applied AC/DC electric field,by using electrochemical impedance spectroscopy(EIS),cathodic polarization curve,scanning electron microscope(SEM),energy spectrum analysis(EDS)and other methods.The results show that the corrosion rate of A6082-T6 aluminum alloy accelerates with the thinning of the liquid film and the applied AC/DC electric field.Meanwhile,the corrosion rate of aluminum alloy increases as the intensity of the applied direct electric field increases.In addition,the applied electric field significantly changes the local corrosion morphology of aluminum alloy,and the corrosion morphology is changed from pitting corrosion to severe exfoliation corrosion after immersion test.According to the results of No.20 carbon steel and galvanized steel,both corrosion rate shows an increasing trend with the decrease of thickness of the thin liquid film.Moreover,both corrosion rate in 3.5 wt.% Na Cl bulk solution is significantly lower than that under the thin liquid film,and the maximum value of corrosion rate occurs when the thin liquid film thickness is around 70 ?m.The rust on No.20 carbon steel under thin liquid film is mainly divided into two layers,namely a loose and porous outer layer and a relatively dense inner layer,but the protection of rust to carbon steel substrate is unsatisfied.The localized corrosion of galvanized steel in thin liquid film is more serious than that in bulk solution.With the application of AC electric field,the galvanized steel cathode current density and the corrosion rate increase with the increase of electric field intensity.