Plasma electrolytic oxidation of AZ31 and AZ91 magnesium alloys:Comparison of coatings formation mechanism

作     者：A.G.Rakoch E.P.Monakhova Z.V.Khabibullina M.Serdechnova C.Blawert M.L.Zheludkevich A.A.Gladkova A.G.Rakoch;E.P.Monakhova;Z.V.Khabibullina;M.Serdechnova;C.Blawert;M.L.Zheludkevich;A.A.Gladkova

作者机构：aDepartment of Metal Protection and Surface TreatmentNational University of Science and Technology‘MISiS’Leninskiy prospekt 4119049 MoscowRussia Helmholtz-Zentrum GeesthachtCentre for Materials and Coastal Research GmbHMax-Plank Str.l21502 GeesthachtGermany Faculty of EngineeringKiel UniversityKaiserstrasse 224143 KielGermany 

出 版 物：《Journal of Magnesium and Alloys》 (镁合金学报（英文）)

年 卷 期：2020年第8卷第3期

页      面：587-600页

核心收录：

学科分类：080503[工学-材料加工工程] 08[工学] 0805[工学-材料科学与工程（可授工学、理学学位）] 

基　　金：The authors would like to thank ACTICOAT project in frame of Era.NET-Rus+Call,2017(Project N477) RFBR(Project No.18-53-76008)in the frame of project ACTICOAT(Era.Net RUS Plus Call 2017,Project 477)for the partial financial support of this work.MS,MZ and CB additionally appreciate European project FUNCOAT("Development and design of novel multiFUNctional PEO COATings"in frame of H2020-MSCA-RISE-2018 call,Grant Agreement No 823942)for the financial assistance 

主　　题：Plasma electrolytic oxidation Magnesium alloys Coating formation Coating growth Corrosion resistance. 

摘      要：The growth kinetics of PEO coatings on AZ31 and AZ91 magnesium alloys were studied and correlated with their structure,compositions(phase and elemental)and corrosion *** was established that the coatings have a two-(outer and anodic)or three-layer structure(outer,inner and anodic)depending on the treatment ***,at short treatment time only an anodic layer and outer layer *** of the outer PEO layer takes place due to the micro discharges,which occur in vertical pores and voids with spherical *** the time is increasing,and electrolyte inside of the pores is heating-up,etching of the Mg substrate and oxide film becomes more dominant and horizontal pores in the interface between coating and metal are *** the pores new anodic layer will form and at this time the formation of the third inner layer *** growth of the inner layer happens via the anodic film as a result of micro discharge ignition in the horizontal pores,accompanied by formation of plasma in numerous micro-voids of this *** coatings formed on AZ91 alloy are denser,than those on AZ31,which is related to the difference in the rates of inner layer growth and dissolving of oxides which are located at the bottom of the horizontal *** of the lower Al content,the AZ31 substrate itself and the also the oxide films are less stable and tend to dissolve at a higher rate compared to ***,it was demonstrated that a good corrosion resistance of the coatings was only obtained on AZ91 and if the average thickness of the coating is around 50μm,correlating with the formation of a sufficiently dense inner laye-Knowing this mechanism,a new two-step treatment was suggested,combining the standard PEO treatment with a subsequent PEO process in an electrolyte supporting the inner film *** concept was successfully applied and a further improved corrosion resistance was obtained compared to the single stage PEO *** improvement of corrosion re