Application Of Micro-arc Oxidation In Aluminum Alloy Piston Of Marine Diesel Engine

The aluminum piston is a component in the four-stroke marine diesel engine and its working conditions are severe and complex. Micro-arc oxidation can generate dense ceramic membrane on aluminum, magnesium, titanium and their alloys to improve surface quality including high hardness, wear resistance, corrosion resistance and thermal shock resistance etc. In this paper, micro-arc oxidation is used to fabricate a layer of dense ceramic coating which can greatly improve performance and service life of aluminum alloy pistons.In this paper, the square-wave narrow pulses dc power is chosen to reduce the consumption of micro-arc oxidation. Adopting the orthogonal experiment method, the optimal formula of electrolyte are 8g/L forNa2Si03,2-3g/L for KOH,2g/L for Na2WO4, 2ml/L for H2O2 and2g/L for EDTA2Na. Because the power supply used in this test are easy to be realized the constant voltage control, the voltage is chosen as a factor of orthogonal experiment design. The optimal result for voltage is 500V～550V. Based on the optimal electrolyte formula and voltage, the optimal result is that frequency is 600Hz, duty cycle 1/20 and oxidation time 50 min. Under the optimal conditions, dense ceramic coating is got with its thickness which is more than 20μm and micro-arc oxidation current density remains at the level of 1 A/dm2.Superior ceramic coatings are got through adding nano-particles of molybdenum disulfide and alumina into the optimized electrolyte.The result of insulation test shows that, after micro-arc oxidation treatment, the sample of piston possesses good insulating properties. After thermal shock tests from 600℃to 10℃for ten times, micro-arc oxidation film remains intact without any cracks and shedding. The results of friction and wear test show that the samples treated by micro-arc oxidation have better properties in friction coefficient and weight loss than the untreated ones under the conditions of both dry friction and oil lubrication. The samples which are obtained in the electrolytes that are added nano-particles of molybdenum disulfide and alumina have much more excellent anti-wear properties than other samples.