Preparation And Properties Of Micro-arc Oxidation Composite Coatings On Magnesium Alloys

Compared with other common metals,magnesium alloys can be said to be the fastest growing metal materials for modern industrial applications.The reason is that they have many advantages.However,magnesium alloys have relatively poor corrosion resistance and are highly susceptible to corrosion in many media,which limits their further widespread use.Therefore,in order to improve the corrosion resistance of magnesium alloys,the study of surface corrosion protection of magnesium alloys is very important.The surface coating not only provides good corrosion protection to the substrate,but also has a decorative and beautifying effect.In this paper,the micro-arc oxidation technology and electro-deposition were employed to prepare the micro-arc oxidation/graphene oxide composite coatings?MAO/GO?on magnesium alloy,and the micro-arc oxidation/cetyltrimethoxysilane self-assembly composite coatings?MAO/HTDMS?of magnesium alloy were prepared by micro-arc oxidation technology and self-assembled technology.The microstructure of the two composite coatings was analyzed by means of SEM,XRD,XPS,EDS,respectively.It could be seen that the micro-arc oxidation/graphene oxide composite coatings were uniformly dense,and the graphene oxide had the layered fold structure.The micro-arc oxidation/self-assembled coatings were also uniformly covered on the micro-arc oxide film and well-produced.The two composite coatings mainly contain elements such as C,O,F,and Si.At the same time,the thickness,roughness and contact angle of the two composite films were tested.The results showed that theroughness of the micro-arc oxidation/graphene oxide composite coatings was 0.355?m,and the roughness of the micro-arc oxidation/self-assembled composite coatings was 0.348?m.They were all smaller than the micro-arc oxidation film which was 0.453?m.The thickness of the graphene oxide layer in the micro-arc oxidation/graphene oxide composite coatings was 6.8?m,and the thickness of the micro-arc oxidation/self-assembled composite coatings was 4.8?m.Because the graphene oxide was hydrophilic,the contact angle of the micro-arc oxidation/graphene oxide composite coatings was 56.14°.The contact angle of the micro-arc oxidation/self-assembled composite coatings was 145.07°and it was very hydrophobic.The electrochemical impedance spectroscopy and polarization curves were used to test the corrosion resistance of the two composite coatings.The results showed that the two composite coatings had higher impedance value than the magnesium alloy substrate and the single micro-arc oxidation film.And in the polarization curve analysis,the corrosion current densities of the two composite coatings reached 8.115×10^-8 A·cm^-22 and 1.314×10^-8 A·cm^-2 that was smaller two orders of magnitude than that of the magnesium alloy substrate and the single magnesium alloy micro-arc oxidation film.The composite coatings had good corrosion resistance.Finally,the corrosion extension process of micro-arc oxidation composite coatings was analyzed by soaking experiments and salt spray corrosion experiments.The results showed that the micro-arc oxidation/graphene oxide composite coatings after soaking,corrosion resistance decreased rapidly,while the magnesium alloy micro-arc oxidation/self-assembled composite coatings had good corrosion resistance.The corrosion resistance of magnesium alloy micro-arc oxidation/self-assembled composite coatings in corrosive media was better than that of micro-arc oxidation/graphene oxide composite coatings.