Preparation And Wear Resistance Optimization Of Micro Arc Oxidation Self-lubricating Ceramic Coating On 2A50 Aluminum Alloy

Micro arc oxidation is a kind of material processing technology,which can induce high energy micro arc plasma and realize the ceramic surface of valve metal by applying high pulse energy between anode and cathode and electrolyte.It can effectively solve the problem of poor tribological performance of light metal material aluminum alloy.In this paper,the wear-resistant ceramic layer on the surface of 2A50 aluminum alloy was formed in situ by micro arc oxidation technology with bipolar pulse power supply.The microstructure,element content and distribution,phase composition,hardness and wear resistance of the ceramic layer were characterized by scanning electron microscope（SEM）,energy dispersive spectrometer（EDS）,X-ray diffraction（XRD）,Vickers hardness tester,profilometer and ball-on-disk friction and wear tester.The following conclusions can be obtained:（1）The influence of cathodic voltage（0 to-200 V）on the ceramic layer was investigated.The results show that the ceramic layer is mainly composed of γ-Al₂O₃ phase;with the increase of cathodic voltage,the compactness and hardness of the ceramic layer first increase and then decrease.When the cathodic voltage is-100 V,the remelting and cutting effect of cathodic voltage greatly optimizes the microstructure of the ceramic layer and the crystallinity of alumina.At this time,the ceramic layer is the most compact,the hardness is the largest（1321 HV0.5）,and the friction coefficient curve is the most stable,the ceramic layer has the best wear resistance.（2）The effect of the positive duty ratio（5 % to 25 %）on the ceramic layer was investigated.The results show that the main components of the ceramic layer are α-Al₂O₃ andγ-Al₂O₃.When the positive duty ratio is less than 25 %,the unstable γ-Al₂O₃ gradually changes into stable α-Al₂O₃ with the increase of duty ratio,and the structure of the ceramic layer is gradually dense.When the duty cycle is more than 25 %,the compactness and crystallinity of the ceramic layer are reduced;when the duty cycle is 25%,the hardness of the ceramic layer is the largest（about 1107 HV0.5）,the wear rate is low(about 2.67× 10^-10cm³（N·m）^-1),the wear surface is regular and shallow,and the comprehensive wear resistance is the best.（3）In order to reduce the friction coefficient of the ceramic layer and the wear of the wear parts,we investigated the effect of the amount of nano molybdenum disulfide（0 g/L to 8g/L）on the self-lubricating ceramic layer.The results show that the response voltage andcritical breakdown voltage are increased,the thickness of ceramic layer is increased,and the self-lubricating ceramic layer is mainly composed of α-Al₂O₃,γ-Al₂O₃ and Mo S2 phases.A large number of molybdenum disulfide particles with uniform distribution were detected in the ceramic layer.When the amount of particles is 4 g/L,the surface of ceramic layer is smooth and compact,the scale of protective lubricating film formed between ceramic layer and wear parts is the largest after friction and wear test.The average friction coefficient is the lowest,（about 0.1712）,the wear amount is the lowest(about 0.53 × 10^-9cm³（N·m）^-1),and the wear resistance is the best.