| The micro-arc oxidation process has the advantages of simple procedures and strong adaptability,and is one of the new technologies of magnesium alloy surface modification.The magnesium alloy parts after micro-arc oxidation treatment have a good combination of surface coating and magnesium alloy substrate,high hardness,excellent wear resistance and strong protection,and have the feasibility of becoming a lightweight component of agricultural equipment.However,the surface of the coating has a volcanic porous structure.In harsh agricultural conditions,the corrosive medium can easily reach the substrate through these micropores,forming galvanic corrosion,resulting in component failure.Therefore,improving the microporous structure of the coating and reducing the porosity have become the key to the technology in the lightweight practice of agricultural equipment.In view of this,this paper takes AZ31B magnesium alloy as the research object,and studies the microstructure,mechanical properties and corrosion resistance of the coating by doping micro-nano TiO2 particles.The specific contents and results are as follows:(1)Control and optimization of micro-arc oxidation ceramic membrane micro-topography.Using the optimized electrolyte formulation in the previous period,using the thickness of the ceramic film and the surface roughness as evaluation indicators,select the oxidation time(min),current density(A/dm2)and frequency(Hz)as factors,and select L9(3)4 The orthogonal table optimizes the design of the experiment.The optimal parameters for the test are as follows,the frequency is 800Hz,the current density is 6A/dm2,and the oxidation time is 30min.(2)Characterization of the ceramic film layer after adding TiO2 nanoparticles.According to SEM tests,after adding TiO2 nanoparticles,the porosity of the surface of the film layer is reduced,and some pores contain agglomerated TiO2 particles;comprehensive XRD and EDS analysis shows that TiO2 in the electrolyte not only participates in the film layer construction,but also enters In the pores of the membrane.The phase composition of the ceramic membrane layer is changed to form a composite ceramic membrane with MgO,MgAl2O4,Mg3(PO4)2,MgSiO4 and TiO2 as the main components.(3)To study the influence of micro-nano-TiO2 film structure and performance.Based on the above optimized process parameters,the electrolyte is doped with nano-scale TiO2 at concentrations of 0g/L,1.5g/L,3.0g/L,4.5g/L,6.0g/L,etc.for sample preparation and Detection.The results show that under the same conditions as other conditions,with the increase of TiO2 concentration in the electrolyte,the growth rate of the ceramic film layer increases significantly,the bonding force between the film layer and the substrate is good,the film layer hardness increases,and the surface is rough Degree,friction coefficient and corrosion rate are reduced accordingly;but when the TiO2 concentration reaches 4.5g/L,further increase the concentration,the hardness of the film is basically unchanged.(4)Comprehensive analysis of the micro-arc oxidation coating layer micro-morphology,performance and phase composition under different TiO2 concentrations,found that high hardness,high wear-resistant TiO2 particles are the key to improve the performance of the coating.It not only improves the phase composition of the membrane layer,improves the performance of the membrane layer,but also blocks holes and cracks,reduces surface roughness,and improves the corrosion resistance of the membrane layer;it also acts as a solid lubricant Effect,reducing the friction coefficient of the film.In the electrolyte system used in this study,when the concentration of TiO2 particles exceeds 4.5g/L,a large amount of deposition or agglomeration occurs in the electrolyte.At this time,continue to increase the concentration of TiO2 particles,the microstructure of the film surface has not changed significantly,and various performance indicators tend to stabilize.In summary,the doping of micro-nano TiO2 particles in the electrolyte can significantly increase the growth rate,hardness,and binding force of the micro-arc oxide film,and reduce the surface roughness,friction coefficient,and corrosion rate.However,the mechanism of micro-nano TiO2 particles participating in film formation,sealing mechanism and how to increase the effective concentration of the particles according to different electrolyte systems need further study. |
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