| With many excellent properties, such as good polishing performance, low porosity and higher corrosion resistance, low-contained tin copper-tin alloy is often used as the matrix metal in the electro deposition wear and friction reducing composite coating.Copper-tin-based graphite composite coatings are an excellent self-lubricating material, which were usually prepared by adding graphite powder into the electroplating bath. The incorporation of graphite Sol in the electroplating bath by pulse electrodepositing can overcome the shortcomings of poor wettability of graphite powder, difficult to disperse and obtain the nanoscale graphite particles. Also this paper analyzed Cu-Sn-graphite composite coating's deposition mechanism, deposition rate, tissue components, surface morphology,microhardness, corrosion, tribological properties and wear mechanism.In this paper, graphite Sol is obtained by electrolysis graphite plate method. The transmission electron microscopy (TEM) analysis test results show that Sol particle size is mainly concentrated between 10nm and 20nm, the particles in the Sol and plating solution are uniformly dispersed and have no obvious agglomeration. Cu-Sn-graphite composite coatings were prepared by adding the graphite in the form of Sol to the plating solution which was based on the pyrophosphate-stannate plating solution. As examined with SEM and EDS,graphite Sol can not only improve the surface quality of Cu-Sn alloy coating, but also obtain the coating with surface smooth, good compactness and no obvious pinhole coating and pitting. At the same time, its carbon content can reach 5.22%. The research of micro hardness results show that the hardness value of graphite Sol composite coating with graphite Sol is lower than that of Cu-Sn alloy. When the addition of Sol is 1 10mL/L, the current density is 2.0A/dm2, and the hardness value is 352.85HV. The minimum corrosion current density of the composite coatings is 1.675×10-5 A·cm-2. Also the Cu-Sn-graphite powder composite coating was prepared to analyze its basic properties. The results of the study show that graphite powder composite plating surface of poor quality, most specimens have bulge phenomenon. The maximum hardness of composite coatings is 328.87HV, while the minimum corrosion current density is 1.782×10-5 A·cm-2. Compared to the composite coating graphite powder, composite coating with graphite Sol has more excellent surface quality,microhardness and corrosion resistance.In order to further enhance the microhardness and wear resistance of the Cu-Sn-graphite composite coating, the Al2O3 Sol was added to the bath. The Al2O3 Sol is obtained by organic salt solution, and the mean diameter of Sol particle size is about 19nm, which is dispersed evenly, easy to deposit and stable. TEM analysis shows that Al2O3 Sol and graphite Sol in the bath can better coexist. SEM and EDS spectrum shows that the addition of nanoparticles increases the density of composite coating, when the concentration of Al2O3 Sol is 40mL/L,the content of the Al element in the coating can reach 0.85%. Because of its physical characteristics and dispersion strengthening effect of nano Al2O3 particles, the microhardness and corrosion resistance of composite coating have been significantly improved. Maximum hardness of composite coatings is 456.15HV. The minimum corrosion current density is 0836 X 10-5A·cm-2.Study on the tribological properties of Cu-Sn-graphite and Cu-Sn-Al2O3-graphite composite coatings shows that the addition of graphite significantly reduces the friction coefficient of Cu-Sn alloy. Under the pressure of 1N point contact dry friction, the friction coefficient can reach 0.1, but because of its low hardness, so the wear resistance needs to be strengthened. SEM observation shows that the wear mechanism of graphite composite coating is abrasive wear and slight adhesive wear. After adding Al2O3 Sol, the wear resistance of coating was obviously improved under the condition of little influence on friction coefficient,and the wear resistance and friction reducing property of composite coating was better. The wear mechanism of Cu-Sn-graphite-Al2O3 composite coating is abrasive wear and adhesive wear. |
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