Study On Micro-arc Oxidation Nano-ceramic Coatings Formed On Cast Aluminum Alloys And Its Properties

Cast aluminum alloys were widely used on high-speed rail catenary parts.However,the poor corrosion resistance and wearing properties greatly hindered its application.Nowadays,heat oxidation and hard anodizing were used to for the modification of its surface properties.But,they are not of ability to protect the alloys in harsh corrosion atmosphere.Micro-arc oxidation,emerged as a new surface treatment technology,can produce dense ceramic coatings with good anti-corrosion and anti-wearing properties on the alloys in a simple and healthy way.In this study,the ZL101A aluminum alloy were used as the substrate alloy to prepare micro-arc oxidation nano-ceramic coatings to improve catenary surface hardness and corrosion resistance,greatly improve the service life of the parts.The microstructure and phase composition of micro-arc oxidation coatings were analyzed by SEM,EDS,XRD and XPS;The hardness,thickness,friction and wear properties of the coatings were measured by microhardness tester,thickness tester and friction and wear tester;Study on corrosion resistance and corrosion mechanism of micro arc oxidation coatings by electrochemical workstation and salt spray corrosion chamber.The final purpose of the research of micro arc oxidation is through the study of test parameters,improved the electrolyte formulation,through an optimization of electrical parameters and the appropriate selection of additives,preparation of ceramic coating with excellent performance.The main work of this paper includes:(1)We study the properties of the coatings formed on ZL101A aluminum alloy,then,we chose the silicate-based electrolytes as the objective.Then through orthogonal tests,we improve the composition of the electrolyte.Single factor test was used to study the effect of one electric parameter(frequency,duty cycle,current density and oxidation time)on the properties of the coatings.The results showed that the most superior properties of the coating were formed under the condition of 18g/L Na2SiO3 + 3g/L KOH + 4g/L NaF and the frequency was set at 400Hz,the duty cycle was set at 50%,the current density was set at 16A/dm2,the was set at oxidation time 40min.And it was of microhardness of 1468HV and corrosion current density of 6.233 X 10-8A/cm2.(2)The properties of the MAO coatings were additionally improved by the addition of nanoadditive TiO2 and Al2O3.And its corrosion properties and corrosion mechanism were investigated by salt immersion test.The results showed that the coating were more compact and of more a-Al2O3 when the additive was Al2O3,and the most superior HV(2341HV)and corrosion current density(1.819×10-9A/cm2).(3)Because there were many factors affecting the MAO and general test methods difficulty to obtain a high parameter optimization,repeatability test in large quantity.According to previous research,introduced an analysis method based on artificial neural network-particle swarm optimization algorithm,the optimal extraction process parameters were from the existing technological parameters,to make coating performance prediction and process optimization.The results show that both the convergence speed and the precision of optimization are satisfactory by using the artificial neural network particle swarm optimization algorithm,and the optimized corrosion current density was 5.679×10-8A/cm2.(4)Salt spray test showed that the micro-arc oxidation coating were of superior anti-corrosion properties among heat oxidation and hard anodizing coatings,And apply it to the high-speed rail catenary parts。Micro-arc oxidation nano-ceramic coatings were prepared in this paper,can greatly improve the high-speed railway catenary of the surface hardness and corrosion resistance,greatly improve the service life of the parts,thereby saving resources and energy,effectively improve the safety of high-speed rail,and shortening foreign similar products level,enhanced related industry competitive advantage.It shows the greatly application potential.