With the basic equipment of national economic development, pressure vessel is widely used in the sector of petroleum, chemical, energy and other industries. However, due to the complex working environment, the surface of the equipment is easy to generate mechanical scratches, corrosion and wear defects, which affect the service life of the plate. As a rapid prototyping technology characterized by low temperature and solid deposition of powder, cold spraying technology has been widely used in additive manufacturing, anti-corrosion coating preparation, repair and remanufacturing. In this paper, pure Al coating and Al-Ni composite coating are prepared on the surface of Q345R steel by adding different contents of Ni powder in cold spraying Al powder. The influence of Ni powder particles in terms of the bonding strength and corrosion resistance of the coatings is systematically studied. Pure Aluminum, Al-10wt.%Ni, Al-15wt.%Ni and Al-20wt.%Ni coatings (The following was called Al coating and Al-10Ni, Al-15Ni, Al-20Ni composite coatings) are prepared by cold spraying on Q345R substrate. The microstructure, porosity, bonding strength and corrosion resistance of the coating are tested by SEM observation, XRD analysis, tensile test, electrochemical test and weight loss test. The results show that the plastic deformation of Al particles increases and the porosity of the coating decreases due to the tamping of Ni particles. With the increase of Ni particles content, the coating becomes more compact. The porosity of Al coating and Al-10Ni, Al-15Ni, Al-20Ni composite coatings are 5.8%, 1.5%, 1.0% and 0.8%. The bonding strength of Al coating and Al-10Ni, Al-15Ni, Al-20Ni composite coatings are 14.6, 15.2, 31.0 and 22.0 MPa. During the deposition process, the impact of Ni particles makes the interface bonding area between the coating and the substrate become bigger. On the other hand, some Ni particles embedded in the surface of the substrate have a pinning effect on the interface between the coating and the substrate, and these conditions are favorable for increasing the bonding strength. Corrosion weight loss test and electrochemical test are used to evaluate the corrosion resistance of the coating. The conventional three-electrode system is used in the experiment, and the scanning frequency is 0.01~105 Hz. The samples are encapsulated with epoxy resin, and the 3.5% sodium chloride solution is for test. According to the actual application environment of Q345R steel, the solution is added with acetic acid to adjust the pH value to 2.8. It can be found that the corrosion weight loss rates of Q345R steel substrate, pure Al coating, Al-10Ni, Al-15Ni and Al-20Ni composite coatings are 2.95, 0.26, 2.38, 1.32 and 1.34 g/(cm2·a). The corrosion weight loss rate of the four coatings is lower than that of Q345R steel, which indicates that both pure Al coating and Al-Ni composite coating can effectively protect the substrate material. However, compared with pure Al coating, the corrosion weight loss rate of Al-Ni composite coating increases possibly due to the existence of potential difference between Al element and Ni element in Al-Ni composite coating, which is easy to form galvanic corrosion and promotes the corrosion of Al element in the composite coating. Zview software is used to fit the electrochemical test results, and the electrochemical test results are consistent with the conclusion of corrosion weight loss test. Compared with Q345R substrate, pure Al coating and Al-Ni composite coating have better corrosion resistance, which can effectively prevent the corrosive medium from contacting directly with the substrate and prevent the substrate from being corroded. In practical engineering applications, Q345R steel has high requirements for comprehensive indicators of corrosion resistance and bond strength. This paper systematically compares the bonding strength and corrosion resistance of composite coatings with nickel content of 10%, 15% and 20%. The results show that when nickel content is 15%, the composite coating has the best bonding strength and corrosion resistance, which provides data to evidence the preparation of protective coatings for pressure vessels. © 2022, Chongqing Wujiu Periodicals Press. All rights reserved.
