| Cast aluminum is the most widely used piston material.Cast aluminum is prone to erosion and thermal cracking during use,resulting in the failure of the piston.Anodic oxidation and Air gap thermal transfer can only solve this problem to some extent.The combustion chamber temperature of the natural gas engine is about 150?,it is higher than that of the conventional fuel engine.The traditional surface treatment technology can no longer meet the requirements of the piston.In this paper,micro arc oxidation technology is applied on the surface of aluminum piston material to prepare CeO2 particles doped micro arc oxidation ceramic coating with heat insulation.It can provide technical support for meeting the requirements of aluminum alloy piston in natural gas engine.The main salt concentration(Na3PO4 concentration and Na2SiO3 concentration),current density,oxidation time and occupation ratio of ZL108 aluminum alloy piston material were studied by orthogonal test.The influence of each factor on the micro-hardness and thickness of the coating was obtained through the range analysis and the results showed that:as the concentration of Na3PO4 increased,the micro-hardness of the coating gradually increased,but the thickness gradually decreased.With the increase of Na2SiO3 concentration,current density,oxidation time and duty cycle,micro-hardness of the correspond coating showed increase and then decrease trend,while the corresponding coating thickness was increase continuously.Variance analysis results showed that the concentration of Na3PO4 had a significant effect on the coating hardness,and the oxidation time also had a significant effect on the coating thickness.The ZL108 aluminum alloy optimum technological parameters of micro-arc oxidation coatings of comprehensive properties:Na3PO4 20 g/L,Na2SiO3 6 g/L,current density 6A/dm2,oxidation time70 minutes and duty cycle 85%respectively,under the conditions of this experiment.On the basis of optimizing the technological parameters,by adding different concentration of CeO2 particles(Og/L,2g/L,4g/L,6g/L and 8g/L)in the electrolyte,the effect of CeO2 particle concentration on the oxidation voltage,hardness,thickness,roughness,corrosion resistance,surface morphology,cross-section topography,element distribution,phase composition,thermal shock resistance,thermal shock resistance and thermal insulation properties of ZL108 aluminum alloy micro arc oxidation coating was studied.The results showed that the oxidative voltage increased first and then decreased with the increase of CeO2 particles concentration.The CeO2 particles controlled the intensity of the discharge by varying the oxidation voltage,and influenced the severity of the arc discharge,which resulted in in an increase first and then decrease in the hardness and thickness of the coating following with the increase of CeO2 particles concentration.The micro arc oxidation coating of CeO2 particles has porous structure,and the surface microporous diameter,sintering disc size and roughness first increase and then decreased.Metallurgical bonding between coating and substrate was observed.And the combination of membrane is mainly composed of y-Al2O3,SiO2.Although the content of Ce element in the coating is relatively small,it is distributed evenly and mainly in the form of Ce02.CeO2 is combined with the melting oxide to block the migration of the molten oxide grain boundary,which reduced the grain size of the coating.At the same time,the antioxidant performance of the coating was improved,and the composite coating with the molten oxide and CeO2 showed excellent thermal shock resistance.It was found that the appropriate concentration of CeO2 had a positive effect on the improvement of the comprehensive performance of the coating.When the concentration of CeO2 particles was 4g/L,the coatings attained the best comprehensive performance. |
PDF Full Text Request