Fabrication And Corrosion Behavior Of LDHs-SDS Film On Magnesium Alloy

As a lightweight structural material,magnesium alloy has a wide application prospect in aerospace,automotive,electronic products and biomedical materials due to its numerous advantages.However,the poor corrosion resistance of magnesium alloy in service environment greatly limits its large-scale applications in industry.At present,surface treatment is the most effective and frequently-used method to improve the corrosion resistance of magnesium alloys.Layered double hydroxides(LDHs)film,as an environmentally friendly protective film,has attracted extensive attention from researchers due to its unique layered structure,interlayer anion exchangeability and good adhesion with magnesium alloys,which has bright development prospects in the field of corrosion protection of magnesium alloys.In this study,a series of anion-intercalated LDHs films and PEO/LDHs composite films were prepared on the surface of AZ31 magnesium alloys respectively by the combination of co-precipitation and hydrothermal growth,and plasma electrolytic oxidation(PEO)plus hydrothermal growth.The microstructure,chemical composition and structural characteristics of different LDHs films and PEO/LDHs composite films were systematically studied by XRD,FT-IR,XPS and SEM.The corrosion behaviors of different protective films were systematically studied by potentiodynamic polarization curves,long-term EIS monitoring and immersion hydrogen evolution experiments,and the corrosion protection mechanisms of different protective films were discussed and analyzed in detail.The main results of this paper are as follows:(1)Sodium dodecyl sulfate(SDS),a green corrosion inhibitor,was successfully introduced into the LDHs film for corrosion protection of magnesium alloys.Three different anion-intercalated Mg-Al LDHs films of nitrate ion,molybdate ion and SDS were prepared on the surface of AZ31 magnesium alloy by a combination of co-precipitation and hydrothermal growth method,respectively.The three LDHs films completely and densely grow on the magnesium substrates,closely adhere to the substrates.The LDHs films are composed of nano-sized LDHs nanoplates,and the thickness of the three LDHs films is about 20?m.(2)The results of electrochemical and hydrogen evolution tests show that the prepared three LDHs films significantly improve the corrosion resistance of magnesium alloys.Compared with the bare magnesium substrate,the corrosion current density of the as-prepared LDHs films decreases by three orders of magnitude,and the corrosion potentials all move to the positive direction.The corrosion resistance of the prepared LDHs films is in the following order:Mg Al-Mo O₄^2--LDHs3^--LDHs2O₄ phases.The LDHs film grown in situ on the surface of PEO film is composed of vertically staggered LDHs nanosheets,and the LDHs nanosheets uniformly and densely seal the microporous defects of PEO film.The LDHs film combines with the PEO film through chemical bonds,and has a strong adhesion.The average thickness of PEO/LDHs composite film is approximately 8?m,while that of LDHs film is about 2?m.(4)The results of electrochemical tests and hydrogen evolution experiments indicate that the prepared PEO/LDHs composite film has excellent long-term corrosion protection performance.The long-term protection performances of the three films are ranked as follows:PEO