Study On Preparation And Properties Of The Micro Arc Oxidation Coating Containing Serpentine On Aluminum Alloy

The working environment of the aluminum alloy piston in the process of service is abominable,not only to withstand high temperature and high pressure,but also to overcome the conditions of wear and strong corrosion.However,the defects such as low hardness,easy wear and poor corrosion resistance of aluminum alloy have restricted the further application of aluminum alloy pistons.Therefore,the reinforcement of the surface of the aluminum alloy piston is of great significance for improving the reliability of cylinder liner and piston assembly of the diesel engine.The micro arc oxidation(MAO)technology can be used to grow a ceramic layer with high hardness,wear resistance and corrosion resistance on the surface of aluminum alloy.Adding serpentine micro-nano particles in the electrolyte is expected to produce a self repairing ceramic composite layer.Therefore,in this paper,the serpentine composite MAO ceramic coating is prepared on the surface of high silicon casting aluminum alloy ZL109 which is applied to the production of the aluminum alloy pistons.First,the process parameters of preparing the MAO coatings containing serpentine micro-nano particles are optimized.Then,the effects of serpentine on the structure,composition and properties of the MAO coatings are investigated.Finally,the friction and wear tests of serpentine composite MAO coatings and cast iron friction pairs are carried out to study the self repairing property of the MAO coatings containing serpentine to the ferrous metal friction pairs.The results show that the optimum process parameters of preparing the MAO coatings containing serpentine under the experimental conditions of this paper are:electrolyte composition and concentration:Na2SiO3 10 g/L,(NaPO3)6 30 g/L,KOH 5 g/L;electrical parameters:unidirectional constant current mode,forward current 8 A,frequency 500 Hz,duty cycle 20%;serpentine concentration 10 g/L;The addition of serpentine micro-nano particles increases the growth rate,final thickness and surface roughness of the MAO coatings,reduces the number of pores but increases the pore size on the surface of the coatings,and increases the density of the coatings;Compared with the MAO coatings prepared without adding serpentine,the hardness and anti wear performance of the MAO coatings prepared with adding serpentine increased by 19.3%and 49.2%,and corrosion resistance of the MAO coatings prepared with adding serpentine improved obviously;The friction and wear tests of the MAO coatings prepared with adding serpentine and nodular cast iron show that the wear weight loss of nodular cast iron disc is reduced by 21.7%,the micro hardness of the worn surface is increased by 19%,and the characteristic elements(Mg element)of serpentine are detected on the worn surface;The friction and wear tests of the MAO coatings which are evenly coated by a layer of serpentine powder and nodular cast iron show that a self repairing protective layer is formed on the worn surface of nodular cast iron discs when the load is 100 N and 200 N.