Study On Optimization Of Electrolyte Formula For Micro Arc Oxidation Ceramic Coating On Cast Aluminum Alloy

ZL109 cast aluminum alloy is featured with low density,good thermal conductivity,small thermal expansion coefficient and high temperature fatigue resistant,which is widely used in the manufacturing of the piston of internal combustion engines.However,ZL109 cast aluminum alloy has a low surface hardness with poor wear resistance,it is inclined to have abrasive damage,ablation and cracks during the operation in severe environment of combustion chamber where the high temperature,high pressure and alternating pressure exist.Considering the damages of the piston are mainly embodied as abrasion and cracks in the top of the piston,a layer of thermal insulation is needed to improve the reliability of the piston.Micro-arc oxidation ceramic film has been produced in large amount to be used as thermal insulation layer.Researches show that the main index that affect the performance of thermal insulation layer is film quality which can be evaluated in many aspects such as film thickness,roughness,tightness and adhere strength.In addition,energy consumption is another important evaluation index in industrial production.In this paper,through the research,we mainly study the optimization of the formulation of the micro-arc oxidation electrolyte in the composite electrolyte system,and find out the electrolyte formulation by which the film thickness is in line with the industrial production requirements and has relatively low energy consumption.In the experiment,the variable control method was used to study the influence of single electrolyte system and composite electrolyte system on the performance of micro-arc oxidation coatings respectively.First,we select sodium silicate,sodium aluminate,sodium hexametaphosphate and sodium phosphate for single electrolyte micro-arc oxidation experiments.According to the results of the experiment,we chose the sodium silicate and sodium aluminate which have better performance in the single electrolyte solution for the composite electrolyte experiments.During the experiment,we evaluated the properties of ceramic film such as film thickness,surface roughness,hardness,film morphology and energy consumption.Based on the evaluation results,the type and proportion of the main filming agents with the best film performance were analyzed,and the formulation optimization of the cast aluminum alloy micro-arc oxidation electrolyte was carried out.The results show that:when the single electrolyte system has the sodium silicate concentration of 7g/L-9g/L,sodium aluminate of 15g/L,the best ceramic film quality can be reached;sodium hexametaphosphate and sodium phosphate are not suitable for the main film forming agent in the concentration range and material selected in this experiment.Experimental results show that the different main film electrolyte formulations will have impact on the ceramic layer thickness,roughness,morphology,energy consumption.And when we took sodium silicate of 6g/L,sodium aluminate of 4g/L as main filming agents,a ceramic film with compact texture,small porosity,dense and uniform micro-morphology could be produced and the thickness of the film conformed to the requirements of industrial production,and its energy consumption is lower.