| Magnesium alloy has the characteristics of low density,high strength and good biocompatibility.It is one of the lightest metal structural materials and exhibits broad application prospects in modern industrial products and biomedical materials.However,poor corrosion resistance severely limits the application range of Mg alloys.In this paper,the nano-composite film is designed and prepared to improve the corrosion resistance of the AZ31 Mg alloy.The microstructure,mechanical properties and corrosion properties of the film are characterized respectively,and the corrosion mechanism of the Mg alloy under the conditions of composite film by surface modification is discussed.The main research conclusions are as follows:(1)The thickness of GaN thin film,Al2O3 thin film and GaN/Al2O3 composite thin film that deposited on the surface of AZ31 Mg alloy by atomic deposition technology are about 20.17 nm,20.14 nm and 20.22 nm respectively.The surface of GaN film is flat and distribute in a network structure.The surface of the Al2O3 amorphous film is smooth and dense without obvious pores and cracks,and the surface of the GaN/Al2O3 composite film is flat and dense,similar to the Al2O3 film.All three films can improve the surface hardness of AZ31 Mg alloy.Compared with GaN film and Al2O3 film,the mechanical properties of GaN/Al2O3 composite film are more excellent.In 3.5 wt.%NaCl aqueous solution,the three films effectively improved the corrosion resistance of the AZ3 1 Mg alloy,and promote the transformation of the corrosion mode from non-uniform corrosion to uniform corrosion.In addition,the GaN/Al2O3 composite film shows better corrosion resistance that it increases the self-corrosion potential of the AZ31 Mg alloy from-1.621 V to-1.326 V,and decreases the corrosion current density from 61.700 ?A/cm2 to 1.457 ?A/cm2.(2)The TiN film with a thickness of about 19.97 nm is deposited on the surface of AZ3 1 Mg alloy firstly by atomic layer deposition technology.The surface of the TiN film is flat without obvious pores and cracks.Subsequently,the TiN/TiO2 composite film is obtained by in-situ oxidation treatment of TiN film and it exhibits no obvious change in surface morphology and thickness.The relative content of TiN and TiO2 can be controlled by adjusting the oxidation time.The experimental results show that the TiN/TiO2 composite film exhibits the best mechanical properties when oxidized for 15 minutes,and the TiN/TiO2 composite film has the best corrosion resistance when oxidized for 20 minutes.The obtained TiN/TiO2 composite film(oxidized 20 min)increased the corrosion potential of the AZ31 Mg alloy from-1.621 V to-1.206 V,and the corrosion current density decreased from 61.71 ?A/cm2 to 0.485 ?A/cm2.(3)As the main preparation technology of nano-films,atomic layer deposition technology has good process repeatability,precise control of film preparation components and thickness,and a good combination with the substrate.By comparing GaN/Al2O3 and TiN/TiO2 nano-composite films,it can be found that the two composite films are interlayer interface structure,which makes the composite film give full play to its mechanical properties.In 3.5 wt.%NaCl aqueous solution,the film interface can effectively prevent the corrosion of Cl ions to AZ31 Mg alloy and the diffusion of Mg ions into the solution.Compared with the GaN/Al2O3 composite film,the TiN/TiO2 composite film shows more excellent corrosion resistance.This is because the two components in the former composite film are obtained by ALD deposition,and the latter composite structure is obtained by In-situ oxidation is obtained,so the interface bonding between the latter components is denser.In addition,in the TiN/TiO2 composite film,when the outer layer of TiO2 is eroded and damaged,the inner layer of TiN oxidation product is TiO2,which can effectively supplement the outer layer of TiO2 and has certain self-repairing properties. |
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