Microstructure Optimization And Tribological Properties Of Ni-SiC-MoS₂ Composite Coating On Aluminum Alloy

Aluminum alloy has become the most widely used light metal structural material in industry because of its high specific strength and good corrosion resistance.However,due to the shortcomings of its low hardness and poor wear resistance,the service life of aluminum alloy workpieces under friction conditions is reduced,which limits its development and application.Electroplating Ni-SiC-MoS₂ composite coating on the surface of aluminum alloy can effectively improve its tribological properties.It is particularly important to obtain a coating with stable quality and good performance because the electroplating process is affected by various conditions.Through further optimization of the process of preparing composite coatings,Ni-SiC-MoS₂ composite coatings with excellent quality and good performance were obtained,and the friction mechanism of the composite coatings was studied.In this work,the effects of pH value,surfactant and sample pretreatment on the surface roughness,hardness and microstructure of Ni-SiC-MoS₂ composite coating were studied.The results show that:When the pH value of the plating solution is 5,the structure of the Ni-SiC-MoS₂ composite coating obtained is uniform,and the surface roughness is smaller than that prepared under the conditions of pH 4 and 6.When anionic surfactant sodium dodecyl sulfate is added to the plating solution,the Ni-MoS₂ composite coating obtained by electroplating is dense and uniform,and the coating is well combined with the substrate,the effect is better than the cationic surfactant cetyl trimethyl Ammonium bromide.Proper galvanizing pretreatment process can effectively improve the bonding quality of Ni-SiC-MoS₂composite coating and substrate.Pre-plating treatment with optimized process,and then electroplating can get Ni-SiC-MoS₂ composite coating with flat appearance,uniform thickness and stable quality,and the coating and substrate are tightly combined.and the optimized pre-treatment process is as follows:sanding with sandpaper?Ultrasonic cleaning?washing with alkaline solution for 30s(60?)?washing with hot water(60?)?wash with acid for 10s?wash with water(room temperature)?first zinc plating for 40s?washing with water(room temperature).In this paper,by comparing the structure and friction behavior of Ni coating,Ni-SiC composite coating and Ni-SiC-MoS₂ composite coating,the strengthening mechanism of MoS₂ in Ni-SiC-MoS₂ composite coating is studied.The results show that MoS₂ plays the roles of dispersion strengthening and grain refinement in the Ni-SiC-MoS₂ composite coating.MoS₂ increases the hardness of the Ni-SiC-MoS₂ composite coating by about 8.6%and reduces the grain size to half compared to those of the Ni-SiC composite coating.In addition,the self-lubricating effect of MoS₂ reduces the friction coefficient of the Ni-SiC-MoS₂composite coating by about 22%and wear rate by about 21%compared to those of the Ni-SiC composite coating.