Corrosion Behavior of Cd-Ti Coating on Landing Gear Surface of 30CrMnSiNi2A Steel in Seawater and Salt Spray

In the research of this paper, 30CrMnSiNi2A, as a commonly used landing gear steel, has to face different environments in the process of use. In the landing gear of amphibious aircraft, the service environment is even worse, and the landing gear has been eroded by spray spatter, salt and alternating dry and wet for a long time. In this paper, the assessment and evaluation system under different environments is established, the immersion and salt spray tests are used to simulate the landing gear environment, the immersion environment is used to simulate the landing gear underwater environment, and the salt fog environment is used to simulate the marine atmosphere and unsteady liquid film environment. The purpose of this paper is to explore the environmental adaptability and failure mechanism of Cd-Ti coating on the surface of landing gear materials for amphibious aircraft. By using hot rolled landing gear steel 30CrMnSiNi2A, the surface was electroplated with Cd-Ti after shot peening, and then passivated. The parallel samples were selected for salt spray test, the coating was measured by EIS under long-period immersion at the same time, and the polarization curves were measured under four kinds of pH conditions. The 3D profile was measured by laser confocal microscope, the surface composition and morphology after 14 days and 28 days after immersion and salt spray test were measured by X-ray diffractometer and scanning electron microscope, respectively, and the energy spectrum was analyzed by EDS. In the measurement of 3D profile, the surface roughness of Cd-Ti coating is Ra=1.69 μm, and the thickness of coating section is about 11 μm. In pH=3.0, the corrosion potential is the most positive and the corrosion current density is the highest. XRD test mainly contains Cd, CdO, Ti and some CdCO3 and CdO2 on its surface. When EIS measurement was carried out in long-period immersion, the Nyquist curve changed with the extension of immersion time. After 28 days, there was a dense corrosion product film on the surface, which could effectively prevent the entry of corrosive media, and the capacitance arc increased in the Nyquist diagram. The weight gain rates of the two experimental environments were measured, which showed that the weight gain rate was faster in the salt spray environment, which was related to the formation of more CdCO3 on the surface. In the salt spray environment, the material surface exists in the form of liquid film, and the supply of oxygen is sufficient, which promotes the oxygen reduction process and the formation of OH‒, a large number of OH‒ also promotes the deposition of corrosion products, and the deposition of corrosion products further adsorbs Cl‒ to make the corrosion front expand forward, which leads to the corrosion rate in the salt spray environment is higher than that in the immersion environment. With the increase of immersion time, the arc resistance radius on the EIS curve increases, the corrosion resistance of the coating becomes better, which is related to the formation of dense corrosion product film on the surface of the coating. With the increase of acidity, the protective ability of Cd-Ti coating to the substrate is weaker. The Cd-Ti coating on the surface of 30CrMnSiNi2A has a good protective effect on the material in salt spray and immersion environment, and can prevent the substrate from corrosion to a certain extent. © 2022, Chongqing Wujiu Periodicals Press. All rights reserved.