Influence Of Cold-sprayed Copper Coating On Corrosion Behavior Of An Assembly Between 6061 Aluminum Alloy And Copper

In metro power supply system,rigid catenary(RC)is a key component to ensure the safe and reliable operation of subway.The RC is a conducting device of a aluminum alloy bus-bar clamping a copper wire,in which current flows from the bus-bar to the copper wire.However,a large potential difference between the aluminum alloy bus-bar and the copper wire is apt to result in the corrosion of the contact parts in a humid and corrosive atmosphere.In particular,the interfacial corrosion of the contact parts leads to a significant reduction in its electrical conductivity,causing a raised energy consumption and safety risk during the working of the subway system.To reduce the interfacial corrosion,a method named“transferring contact interface”is proposed.In this method,a copper coating is deposited on the aluminum alloy surface where is contact with the copper wire to transfer the aluminum-copper contact interface to the copper-copper contact interface.Thus,the potential difference between contact parts is significantly reduced or eliminated,leading to an improved corrosion resistance.In this paper,six groups of cold-sprayed copper coatings were prepared on aluminum alloy substrate by using three kinds of copper powders with different particle sizes and three kinds of powders mixed with different components,and then formed six groups of corresponding connector samples with copper.In addition,connector sample consisted of uncoated aluminum alloy and copper was used as control group.The surface and cross-section of the coating were analyzed by scanning electron microscope(SEM),energy dispersive spectrometer(EDS)and X-ray diffractometer(XRD).It was found that the cold sprayed coating had a layered structure without stainless steel particles deposition,the main defects of the coating were holes and gaps at the interface of particle-particle and coating-substrate,and the particle size of the sprayed powder and the volume fraction of stainless steel particles in the mixed powder had a significant effect on the microstructure of the coating.With the decrease of particle size and the increase of stainless steel particle content in the powder,the density of the coating increases significantly,the porosity decreases significantly,and the adhesion and hardness of the coating increase.Electrochemical corrosion experiments were performed and the result shows that cold-sprayed copper coating on aluminum alloy can significantly improve the comparing open circuit(OCP)and corrosion potential of the contact,reduce the corrosion current density,and improve the corrosion resistance of the contact.The trend of corrosion resistance is negatively related to the porosity.After electrochemical test,corrosion pits and product(Al(OH)₃)appeared on the surface of uncoated aluminum alloy,and the coating surfaces also suffered from different degrees of corrosion.The corrosion spalling phenomenon on the coating surfaces is significantly reduced with the decrease of the porosity of the coating.What's more,because of the gaps in the contact interface between particles,which were easily penetrated by the corrosion medium,the corrosion damage points are mainly distributed around the contact interface between particles.In order to simulate the actual service environment of the RC,the neutral salt spray accelerated test was carried out and the results show that the cold-sprayed copper coating on aluminum alloy can effectively slow down the corrosion of contact interface and reduce the corrosion products.With the decrease of powder particle size and the increase of stainless steel large particle content in the powder,the effect of the corresponding coating on reducing the corrosion of contact interface is better,and the corrosion rate is lower.By analyzing the composition and phase of corrosion products,it was found that the corrosion product on the surface of copper coating is Cu₂O,and that on the surface of aluminum alloy is Al(OH)₃.In addition,it was found that the corrosion product with a certain thickness has a blocking effect on the corrosion medium and provides a period of protection for the matrix.