Preparation And Corrosion Resistance Of LDHs Films On Magnesium Alloy Surface

Magnesium alloys are widely used in automotive,aerospace,electronics and other industries due to their low density,high specific strength,low modulus of elasticity,good impact resistance and shock absorption.However,due to its poor corrosion resistance,the applications of magnesium alloys have been largely limited,so are often surface treated to improve their corrosion resistance.The common method is to prepare films on the surface of Mg alloy substrate,but once the films are destroyed,the substrate will directly contact the environment,leading to corrosion,or even accelerating corrosion.In order to improve the corrosion resistance of the films,it is a trend to synthesize a new type of intelligence films with self-healing,corrosion inhibition and protection properties.Based on the characteristics of the composition and structure of layered double hydroxides?LDHs?and ion exchange,it can provide templates for the preparation of smart coatings with self-healing,corrosion inhibition and protection functions.In this paper,Mg-Al-NO₃ LDHs films was synthesized on AZ91D magnesium alloy by in-situ hydrothermal method.LDHs-WO₄,LDHs-Met,LDHs-Cys and LDHs-Phe films were obtained by inserting inhibitors into the inner layer by virtue of anion exchange process.Mg-Al-NO₃ LDHs,LDHs-Met,LDHs-Cys,LDHs-Phe and LDHs-WO₄ were characterized by X-ray diffraction?XRD?,scanning electron microscopy?SEM?and Fourier transform infrared?FT-IR?.The good corrosion resistance of the coating was clarified by electrochemical,bonding and immersion test methods.The following results were obtained:?1?The Mg-Al-NO₃ LDHs films obtained by hydrothermal method can form a very stable LDHs structure even though the NO₃^-in the interlayer is not an inhibitor ion,which results in a barrier between the substrate and the corrosive medium to inhibit corrosion.Therefore,compared with AZ91D substrate,Mg-Al LDHs film with NO₃^-has better corrosion resistance.?2?LDHs-Met,LDHs-Cys,LDHs-Phe and LDHs-WO₄ films obtained by ion exchange not only have the characteristics of Mg-Al-NO₃ LDHs films,but also have the characteristics of corrosion inhibitors.The results show that the corrosion resistance of LDHs films with inorganic or organic inhibitor ions is obviously improved.?3?The bonding strength between LDHs films and substrate was studied.The results show that the bonding strength of LDHs films obtained by hydrothermal treatment and ion exchange is very good.?4?The self-healing properties of Mg-Al-NO₃ LDHs films were studied.The results showed that the corrosion resistance of Mg-Al-NO₃ LDHs films with artificial scratches was significantly improved after immersion in 3.5 wt.%NaCl solution.