The Effect Of Y₂O₃ Doping On The Characteristics And Mechanism Of The Micro-arc Oxide Film Of Cast Aluminum Piston Material

At present,aluminum alloy pistons have been widely used in the internal combustion engine industry.As the internal combustion engine gradually adopts new fuels such as natural gas,the temperature of the combustion chamber is gradually increased,and the piston is also put forward higher requirements.The shortcoming which the aluminum alloy pistons are difficult to meet the engineering requirements at the high temperature is gradually exposed.In this paper,the rare earth Y2O3 modified ceramic coatings were prepared on the surface of the aluminum alloy piston material by micro-arc oxidation technology,so the surface properties of the aluminum alloy piston material are improved and also prolong the service life of piston material.In this experiment,ZL108 cast aluminum alloy was used as the matrix material,and the effects of the concentration of sodium phosphate,sodium hexametaphosphate,sodium dihydrogen phosphate,sodium pyrophosphate and current density on the properties of micro-arc oxidation coatings on cast aluminum alloy piston materials were studied by orthogonal experiment.Optimal process parameters are filtrated through process optimization.Based on the optimal process parameters,the effects of Y2O3 concentration on the properties of micro-arc oxidation coating of cast aluminum alloy piston material were studied by SEM,EDS,XRD and XPS.The modification mechanism of Y2O3 doped micro-arc oxidation coating was also discussed.The results show that the optimum process parameters for micro-arc oxidation of cast aluminum alloy piston materials are sodium phosphate 12g/L,sodium dihydrogen phosphate 8g/L,sodium hexametaphosphate 8g/L,sodium pyrophosphate 16g/L,current density 20A/dm2 at a temperature of 20±3?,a frequency of 100Hz,a duty cycle of 20%and a time of 30min.In this condition,the thickness and hardness of the coating can be optimized.Under the optimal process parameters,Y2O3 particles of Og/L,1g/L,2g/L,3g/L and 4g/L were added to the electrolyte to study the influence of the characteristics of different Y2O3 concentrations on the properties of micro-arc oxidation coatings on cast aluminum alloy piston materials.Results have shown that with the addition of Y2O3 particles,the oxidation voltage gradually increased firstly and then decreased at Y2O3 concentration of 4g/L.The thickness,hardness,corrosion resistance and heat insulation property of the oxidation coatings showed the same trend with the voltage,which proved that excessive addition of Y2O3 was unfavorable to the performance of the coating.However,as the concentration of Y2O3 increased,the number and size of pores on the coating surface decreased,and the coatings became more smooth and dense.The coatings mainly consisted of Y2O3,?-Al2O3,?-Al2O3 and SiO2,indicating that Y2O3 particles have successfully entered the coating.Combined with XPS analysis,it was found that Y2O3 particles do not undergo redox reaction during the modification process and still existed in the form of Y2O3.After doping Y2O3 particles during the micro-arc oxidation process,the addition of Y2O3 can increase the exchange rate of ions,led to promoting the growth rate of the coating,so the coating thickened to affect its performance.On the other hand,Y2O3 can prevent the growing of ceramic grains during the coating formation process,refined the ceramic structure and obtained a smooth and dense ceramic coating to affect its performance.