| In the subway power supply system,the rigid overhead contact system?OSC?is widely used due to its simple structure,easy installation and maintenance.The OSC consists of collecting bars and contact wires.However,in the wet marine atmosphere environment,there is a large potential difference between the collecting bars and the copper contact wire during the use of the OSC,the contact corrosion is easily occurred.The power consumption of the power supply circuit is seriously increased and cannot be properly serviced.This not only brings security risks to the operation of the subway,but also significantly increases the operating costs of the subway.In view of the above problems,this article started with exploring the corrosion of aluminum alloy-copper contact pieces,and studied the corrosion behavior of aluminum alloy-copper contact pieces to reveal the contact corrosion mechanism.Then,based on the contact corrosion state,which is the main influencing factor of contact corrosion-the surface roughness of the material,two ways to reduce the corrosion behavior of aluminum alloy-copper contact were proposed:?1?Reducing the roughness of the contact surface to reduce the width of the interfacial gap,thus preventing the corrosion medium from entering the gap to improve its corrosion resistance.?2?By electroplating copper on the surface of the aluminum alloy,a copper-copper bond surface was formed between the contacts,thereby reducing the potential difference which is easy to cause corrosion.Through the design of orthogonal test,the influence of matrix roughness,electroplating current density,stirring speed and electroplating time on the adhesion and corrosion resistance of the coating is analyzed,and the parameters of the electroplating process are optimized.Through systematic research,the following results are obtained:The aluminum alloy-copper contact pieces were soaked in 3.5%NaCl solution for different cycles.Under the combined action of galvanic corrosion and crevice corrosion,the corrosion of the aluminum alloy in the contacts was accelerated.?1?It can be seen from the SEM observation that as the etching time is prolonged,the density of the etching pit increases,and the depth of the etching pit increases and the width increases.The corrosion layer thickness increases first and then decreases with the increase of corrosion time.?2?The EDS spectrum and XRD phase analysis show that the corrosion product is mainly Al?OH?3.?3?In the initial stage of corrosion,the corrosive medium penetrates into the contact surface and preferentially stays in the defect,causing oxygen concentration battery and acidification autocatalytic cycle to accelerate corrosion.On the side surface of the contacts,galvanic corrosion occurs at the edge of the contact due to the large difference in corrosion potential between the aluminum alloy and the copper.The corrosion rate keeps rising.During the middle period of corrosion,the corrosion products increased and thickened,hindering the progress of corrosion,and the corrosion rate decreased slightly.In the later period of corrosion,the thickened corrosion product cracks due to internal stress,so that the corrosion continues and the corrosion rate further increases.Throughout the corrosion process,copper is always protected as a cathode during the whole corrosion process.In alternating wet and dry environments,the corrosion resistance of the contacts at different roughnesses was tested.?1?It can be obtained through XRD phase analysis that the corrosion product is mainly Al?OH?3.?2?Electrochemical test results show that the open circuit potential of the aluminum alloy rises from-0.80V to-0.75V as the substrate roughness decreases,and the corrosion current density of the contact decreases from 1.1327×10-3A/cm2to 1.3434×10-4A/cm2,reduced by an order of magnitude.The polarization resistance increased from 2162.93?·cm2 to 16797.26?·cm2.?3?As the surface roughness of the aluminum alloy is reduced,the corrosion resistance of the aluminum alloy-copper contact is also significantly improved.The results of the extreme analysis of orthogonal experiments show that the electroplating current density has a significant effect on the adhesion,corrosion resistance and hardness of the coating.When the electroplating current density is in the range of 0.320.48A/dm2,the coating is smooth and dense,the surface has no scorching,pitting and holes,and the corrosion resistance is optimal,which can significantly improve the corrosion resistance of the aluminum alloy matrix.Therefore,the optimum process plan was determined as:substrate roughness is 0.0371?m;current density is 0.48A/dm2;the stirring speed is 300r/min;time is 30 min. |
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