Corrosion Properties Of AZ31 Magnesium Alloy With Ti And TiN/TiO₂ Film Made By Magnetron Sputtering

Magnesium alloy has the advantages of low density,high specific strength,high specific stiffness and high thermal conductivity.And it is widely used in automotive,aerospace,3C products so on.However,the poor corrosion resistance severely limits the application.In this thesis,micron-sized Ti film and TiN/TiO2composite films were prepared on AZ31magnesium alloy by magnetron sputtering.The morphology,phase,structure and chemical composition of the films were investigated in details,so as to find the suitable preparation.Then the relationship between the mechanical properties,corrosion properties with film microstructure were explored.Structure-mechanical properties/corrosion correlation had been established.Finally,the corrosion mechanisms of AZ31 magnesium alloy with films were discussed.The main conclusions are as follows:（1）Ti films（1～2μm）was deposited on the surface of AZ31 magnesium alloy by magnetron sputtering.As Ti film thickness increasing,the densification increases and surface roughness decreases.Ti film would raise surface hardness,but rarely change Young’s modulus,flexibility.Wear resistance cloud been improved.The corrosion mode keeps in metal corrosion mode,but the corrosion is more uniform.Further more,Ecorr increase from-1.621 V to the-1.112 V and Icorr decrease from61.70μA/cm² to 2.03μA/cm².In the initial stage,Ti film forms a dense and uniform protection on the surface,which stops corrosion medium of corrosion and improves the medium distribution uniformity on the surface.In the middle stage,the corrosion products accumulate and crack,which would lead the corrosion medium to invade,and the corrosion accelerates.In the final stage,stress corrosion cracking would be more serious,spall would also happen,so the corrosion became fast and uniformed.The micron-Ti film can improve the early corrosion uniformity,but works a litter in the latter stages,so the corrosion current density is reduced by～1/10.（2）TiN/TiO2 composite films can be prepared by magnetron sputtering+in-situ oxidation.TiN/TiO2 film is an inter-layer structure.The film is more dense,more uniform,less rough than magnetron sputtering-TiN film.TiN/TiO2 film has a good bond to the substrate.It can slightly improve the hardness,Young’s modulus,flexibility,and significantly improve the wear resistance.TiN/TiO2 film makes the corrosion mode change to Rs(CPE2(Rf（CPE1Rct）,and obviously improves the corrosion uniformity.E_corr increases to-1.272 V and I_corr decreases to 0.974μA/cm².Firstly,TiN/TiO2 film forms a dense and uniform protection.Then,the top laye TiO2in the film would be consumed while the bottom layer TiN transforms into TiO2.Finally,the TiN/TiO2 film is exhausted,magnesium alloy participates in corrosion.But the whole corrosion process would be more uniform.TiN/TiO2 can improve both early and middle stage uniformity of corrosion,and TiN would self-repair TiO2.TiN/TiO2 works better than Ti film as corrosion protect.