Research On Electrical Contace Fretting Wear Behavior And Impact Behavior Of Micro-arc Oxidation Coating

As the most abundant metal element in the earth’s crust,aluminum has high ductility and good plasticity.It has the characteristics of high strength and low density.However,at present,the wear resistance and corrosion resistance of aluminum alloys cannot meet the requirements,and,as mechanical components,it has the defects of soft quality and high friction coefficient,which requires the coating procedure to improve its overall performance.Micro-arc oxidation coating technology is a surface ceramic treatment for light alloys such as aluminum and magnesium.This process is simple with short processing time,and it has no pollution to the environment,which makes it valuable for industrial application.This paper prepared micro-arc oxidation coatings with different surface properties on the surface of aluminum alloys by controlling the micro-arc oxidation time to study fundamental features of the coatings formed at different oxidation times.The electrical contact frett ing wear behavior and impact behavior of the coatings was also investigated in this paper.The main conclusions are as follows:(a)Morphological evolution and compositional changes of micro-arc oxidation coatings with different oxidation timesThe micro-arc oxidation ceramic film prepared by silicate system is mainly composed of Al and O elements,followed by a small number of electrolyte elements K and Si.The content of these four elements varies with the oxidation time.The surface morphology of the coating under all oxidation treatment periods is typical porous morphology,and severe ablation occurred on the surface at 60 min.When the oxidation time is less than 50 min,the thickness of the film increases with time,and the thickness of the coat ing reduces at 60 min due to severe ablation.The micro-arc oxidation film roughness increases with the increase of oxidation time,and the roughness of the oxide film decreases slightly at 50 min.(b)Electrical contact fretting wear behavior of micro-arc oxidation coatings with different oxidation periodsUnder electrical fretting wear conditions,the contact resistance changes of aluminum alloy micro-arc oxidation film formed under all oxidation time can be divided into three stages: insulation stage,contact resistance decay stage,and conduction stage.With the increment of circulation numbers,a region electric leakage phenomenon occurred in the micro-arc oxidation film,which makes the insulation resistance transformed into the contact resistance within the critical period.The rapid degradation of the coating caused the metal matrix to be exposed in vitro at 10 min and 20 min,which led to a sudden drop in the contact resistance.During 30min~70min,the decay period of the contact resistance was extended slightly due to the coating wear rate,and significant fluctuation during resistance drop is generated by the crack initiation extent.With the increase of oxidation time,the friction coefficient of MAO coating has two opposite trends.When the oxidation time is less than 40 min,the friction coefficient decreases with the oxidation time increment.However,when the oxidation time range is 50 min to 70 min,opposite phenomenon ocurred.During the micro-motion process with electric contact,the wear depth of micro-arc oxidation coating decreases with the increment of oxidation treatment time,and the wear resistance increases with it.When the oxidation time reached 60 min,the wear depth of the coating was expanded,and the wear resistance became worse due to surface ablation.Among seven micro-arc oxidation samples,the wear depth of MAO coating suffered 50 min oxidation is the least,with the best wear resistance.(c)Impact behavior of micro-arc oxidation coatings with different oxidation periodsMicro-arc oxidation technology can reduce the kinetic energy loss of materials in impact wear.Different oxidation periods lead to different kinetic energy losses of the coating.With the increment of the oxidation time,the kinetic energy losses of the coating are large at both terminals and low in the middle part,in which the energy dissipation of 2# coating(oxidation time is 30 min)in the central part was the smallest,and the impact rebound rate was the largest.Micro-arc oxidation technology will also increase the contact stress of the material in the impact wear,and the contact stress will increase with the oxidation time.Different oxidation times will cause different micro-bumps on the surface of the MAO coating.When the material is impacted and worn,the impact first contacts with the micro-bumps body on the surface of the MAO coating,and the body will be broken into fragments.These fragments will cover the surface of the impact wear mark under the action of subsequent impact.Micro-arc oxidation techno logy can improve the impact wear resistance of the coating.The wear depth of the MAO coating is the smallest during 30 min oxidation,whose wear profile approaches a straight line,and its impact wear resistance is the best.