Effect Of Surfactants On The Structure And Properties Of LDHs Coating On Magnesium Alloy

Magnesium alloy is the lightest structural metal material(the density is only about 1.8 g/cm3),but its poor corrosion resistance seriously limits its application and development.Surface coating is one of the most effective and economical methods to protect Mg alloys from corrosion.In recent years,the smart LDHs coating with good corrosion resistance has attracted people’s attention.The soft template method which implying surfactant as soft template is one of the simplest methods to synthesize LDHs.The soft template method can control the morphology,structure and size of LDHs.However,so far,no one has studied the effect of surfactant on the synthesis of LDHs corrosion-resistant coating on the metal surface.In this paper,different Mg Al-LDHs coatings were prepared on the surface of AZ31 Mg alloy by introducing different surfactants in the process of hydrothermal coprecipitation,including anionic surfactants(SDS,SDBS,SLS,SLand SM),cationic surfactants(TTAB)and non-ionic surfactants(Span 80).The crystal structure of LDHs were characterized by XRD.The functional group composition of LDHs were characterized by FT-IR.The composition and structure morphology of LDHs coating were characterized by XPS and SEM.The good corrosion resistance of LDHs coating prepared in this paper was clarified by electrochemical test,adhesion test,immersion test and salt spray test.The results are as follows:(1)Different LDHs corrosion resistant coatings with good adhesion to the substrate were successfully prepared on the surface of magnesium alloy by introducing different surfactants in the process of hydrothermal coprecipitation.(2)Whether anionic surfactants could enter the interlayer of LDHs was related to its molecular structure and concentration.(3)Surfactants containing long carbon chains could be adsorbed on LDHs and improve the hydrophobicity of LDHs,so they played a role in hydrophobic modification of the coatings.The contact angle of Mg Al-NO3--LDHs coating was 27.3°,but contact angles of LDHs coatings prepared based with SDS,SDBS,SLS,SL,SM,TTAB and Span 80 were as high as 104.8°,85.3°,99.9°,106.4°,115.4°,64.9° and 80.3°,respectively(4)The introduction of surfactant in the process of hydrothermal coprecipitation could prepare smaller and curved LDHs nanosheets through its soft template,and those small and curved LDHs nanosheets could form a denser LDHs coating.The addition concentration of surfactant had a great influence on the morphology of the LDHs coating.When the addition concentration was low,there were still obvious pores in the LDHs coating.And with the increase of surfactant concentration,the LDHs coating became denser.(5)The corrosion resistance of LDHs coatings prepared with surfactant was much better than Mg Al-NO3--LDHs coating,and their corrosion resistance increased with the increase of surfactant concentration.(6)LDHs coating prepared based on surfactant had better long-term corrosion resistance than Mg Al-NO3--LDHs coating.