The Ceramic Layer On Cylinder Of Whole Aluminum Engine And Its Corrosion Resistance

Cast Al-Si alloys is the preferred material for the lightweight of automotive engine,but the application is limited by its low hardness,dad wear-resistance and poor corrosion resistance.In order to improve the surface properties of Al-Si alloy,a new method of Plasma Electrolytic Oxidation was proposed,however,however,the existence of Si element makes the growth of PEO ceramic layer special,which will seriously affect the compactness and integrity of ceramic layer,and the mechanical properties of PEO ceramic layer will also change greatly.Aiming at this problem,by changing the shape of Si element and adjusting the key power parameters,the growth characteristics and properties of the PEO ceramic layer were studied systematically.The effects of different Si forms on the voltage characteristics,the microstructures,the thickness and the hardness of the ceramic layers were discussed.The corrosion resistance of the ceramic layers was compared and analyzed.The results show that the growth rate of the refined primary Si is higher,the thickness is larger,the microstructure is denser,and the hardness and corrosion resistance properties are improved.Based on the study of voltage characteristics,discharge phenomena,ceramic layer structure and wear resistance during the preparation of PEO ceramic layer,the results show that the thickness and hardness of the ceramic layer increase with the increase of pulse frequency and current density.When the pulse frequency is 1500 Hz,the thickness and hardness of the ceramic layer reach the peak value,coating hardness reached the highest 1100 HV,the negative voltage of the ceramic layer grows rapidly during the growth process,and the wear resistance of the ceramic layer at this time is the best.The hardness and thickness of the ceramic layer prepared by the current density of 14A/dm2 reached the peak,showing the best wear resistance.The corrosion resistance of the PEO ceramic layer under different pulse frequency and current density was studied.the corrosion resistance of the ceramic layer was characterized by dynamic potential polarization curve and salt spray test.The results show that the corrosion current density of ceramic layer prepared by different pulse frequency and current density is lower than the substrate.The corrosion current density of ceramic layer prepared by 1500 Hz frequency and 10A/dm2 current density is 2.980×10-8,2.185×10-8,which is three orders of magnitude lower than that of the base alloy.The 1400 h neutral salt spray test of the ceramic layer shows that the corrosion resistance of the ceramic layer is optimal when the pulse frequency and the current density are 1500 Hz and 10A/dm2.The effects of silicon morphology,pulse frequency and current density on the growth and properties of PEO ceramic layers were obtained,which is important in the application of PEO technology to high silicon aluminum alloys.