Study On Corrosion Behavior Of Microarc Oxidation Graphene Composite Coating On LZ91 Mg Li Alloy

The poor corrosion resistance of magnesium-lithium alloys limits the industrial application of magnesium-lithium alloys.Micro-arc oxidation of magnesium-lithium alloys is an effective method to promote industrial applications.Graphene has many excellent properties such as low resistivity and good electrical conductivity,and adding graphene as an additive to the micro-arc oxidation electrolyte is another hot topic in micro-arc oxidation research.In this paper,a graphene-containing micro-arc oxidation(MAO)film layer was prepared on the surface of LZ91 magnesium-lithium alloy sheet using an alkaline silicate system micro-arc oxidation electrolyte,followed by a double conductive film layer(MAO/CG)and a triple anti-corrosion film layer(MAO/CG/AG)on top of the MAO film layer by immersion.The effects of parameters such as graphene concentration,voltage and time in the micro-arc oxidation electrolyte on the thickness and corrosion rate of the MAO film layer were investigated,and the electrochemical corrosion mechanisms of the MAO/CG double-layer conductive film layer and the MAO/CG/AG triple-layer anticorrosive film layer were given,and the following conclusions were obtained.1.At a microarc oxidation voltage of 250 V and a microarc oxidation time of 600 s,the film thickness δ(μm)showed an exponential relationship with the graphene concentration c(g/L)after a certain amount of graphene was added to the electrolyte:.When the graphene addition is in the range of 0～1.0 g/L,graphene in the electrolyte promotes the growth of the MAO film layer by increasing the electrolyte conductivity,while graphene will enter into the MAO film layer pores and gather into C particles,blocking the pores in the MAO film layer,and the corrosion resistance of the film layer rises.When the concentration of graphene is greater than 1.0 g/L,graphene will increase the dissolution rate of MAO film layer and inhibit the growth of MAO film layer,then graphene will promote the growth of pores in MAO film layer,and the corrosion resistance of the film layer will decrease.2.At an electrolyte of 1.0 g/L graphene and a micro-arc oxidation time of 600 s,the film thickness δ(μm)showed a linear relationship with the micro-arc oxidation voltage E(V):.The voltage promoted an increase in MAO film thickness,and the corrosion resistance first increased and then decreased with increasing voltage.At an electrolyte graphene 1.0 g/L and a microarc oxidation voltage of 250 V,the film thickness δ(μm)shows an exponential relationship with the microarc oxidation time t(s):.The MAO film thickness and corrosion resistance increased from 0 to 300 s.After 300 s,the MAO film growth slowed down and the corrosion resistance decreased.3.The conductive graphene(CG)film layer was prepared on the MAO film layer,and the thickness of the film layer on the surface of the Mg-Li alloy increased to 58μm.The conductive graphene film layer improved both the corrosion resistance of the MAO film layer and the electrical conductivity,and the annual corrosion rate of the MAO/CG double-layer conductive film layer was 0.04 mm/a,and the electrical conductivity was 7.89 Ω-1·cm-1.4.The anti-corrosion graphene film layer(AG)was prepared on the MAO/CG double conductive film layer,the thickness of the film layer on the surface of the magnesium-lithium alloy increased to 81 μm.this anti-corrosion graphene film layer is dense and uniform,with very low electrical conductivity,its conductivity is 4.89 ×10-4 Ω-1·cm-1,preventing the corrosive medium from electron exchange with the substrate,improving the corrosion resistance of the MAO film layer,protecting the substrate from corrosion.MAO/CG/AG three-layer anti-corrosion film layer whose annual corrosion rate is 0.003 mm/a.