| The unique combinations properties of portable,high specific strength,high corrosion resistance provided by aluminum and its alloys make aluminum one of the most attractive and versatile metallic materials.For a board range of uses,from simple foil to complex engineering materials,aluminum and its alloys have a broad application in all kinds of industry field.The poor anti-wear property of aluminum and its alloy limits its application.In order to overcome its shortcoming,researchers used various surface modification methods to strengthen the surface of aluminum and its alloys including chemical oxidation,anodization,thermal spraying,micro arc oxidation and many other treatment technologies.As a new surface treatment technology,micro arc oxidation has the characteristics of simple and high-efficiency process.The MAO coating made by micro arc oxidation is metallurgical bonding with the substrate,and has the characteristics of high density,high hardness and good wear resistance.In this paper,micro arc oxidation(MAO)was used to prepare MAO coating on 6061 aluminum alloy.The concentration of electrolyte was changed to investigate the structure and performance by scanning electron microscope(SEM),x-ray diffraction(XRD),acoustic emission test,abrasion test.A three factor and four level orthogonal experiment was carried out with the concentration of CH3COONa,(NaPO3)6,Na2WO4 as the influence factors.The priority of influence of concentration of CH3COONa,(NaPO3)6 and Na2WO4 on the performance of coating was analysed.Then,the micro-hBN/nano-hBN were added to the electrolyte.The three factor and four level orthogonal test was designed again that the factors still were the concentration of CH3COONa,(NaPO3)6 and Na2WO4.The priority of influence of concentration of CH3COONa,(NaPO3)6 and Na2WO4 on the performance of coating was analysed again.Next,the microstructure,phase composition and properties of the MAO layer with micro-hBN/nano-hBN were compared with the corresponding MAO layer without hBN addition.The best electrolyte composition with hBN was selected.Then,different concentration of hBN was added to the optimum electrolyte.The microstructure,phase composition and properties of MAO coatings with different concentration of hBN were analyzed and the optimum hBN addition was selected.Finally,the optimum composition of the electrolyte and the optimum addition of hBN were combined to form the best formula.Through the above data,the effect of hBN on the coating was analyzed.The results showed that the MAO films prepared by the electrolyte system of CH3COONa-(NaPO3)6-Na2WO4 are mainly composed of Al,α-Al2O3,γ-Al2O3,W.The concentration of CH3COONa had the most obvious influence on the thickness and binding force of the film,and the concentration of(NaPO3)6 had the most obvious influence on the friction coefficient of the film through orthogonal test analysis.hBN-MAO coatings were prepared by the electrolyte with micro-hBN/nano-hBN.hBN-MAO films were composed of Al,α-Al2O3,γ-Al2O3,W,hBN.Over orthogonal test analysis,the concentration of CH3COONa had the most obvious influence on the thickness of micro-hBN-coatings/nano-hBN-coatings;the concentration of CH3COONa and(NaPO3)6 had the most obvious influence on the binding force of micro-hBN-coatings;the concentration of CH3COONa had the most obvious influence on the binding force of nano-hBN-coatings;the concentration of Na2WO4 had the most obvious influence on the friction coefficient of micro-hBN-coatings/nano-hBN-coatings.The optimum composition of the electrolyte was concluded.When adding micro-hBN,9 series of samples had the best tribological properties,the composition of CH3COONa,(NaPO3)6,Na2WO4 was 12g/L,3g/L,3g/L,respectively.When adding nano-hBN,3 series of samples had the best tribological properties,the composition of CH3COONa,(NaPO3)6,Na2WO4 was 8g/L,9g/L,3 g/L,respectively.hBN-coatings were prepared by the optimum electrolyte with different concentration of hBN.The results showed that the optimal micro-hBN and nano-hBN addition was 4.5g/L and 2.5g/L,respectively.With the increase of concentration of micro-hBN/nano-hBN,the thickness and adhesion force of film increased while the tribological performance of film improved as the concetration of micro-hBN/nano-hBN is respectively 0-4.5g/L/0-2.5g/L.But when the concetration of micro-hBN and nano-hBN was respectively over 4.5g/L and 2.5g/L,the thickness and adhesion force of film decreased while the tribological performance of film declined with the increase of concentration of micro-hBN/nano-hBN.So the thickness,adhesion force and tribological performance of film offered upgrade firstly than descending latter tendency.In this paper,various electrolyte concentration were used for micro arc oxidation on 6061 aluminum alloys.The ceramic coatings which has a metallurgy union with the substrate were obtained and effect of electrolyte concentration on microstructure,phase composition and wear resistance of MAO coating was researched.The mechanism and effect of micro-hBN/nano-hBN on properties were discussed.The whole study was expected to lay foundation for the application of the micro arc oxidation technique in relevant industries. |
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