Study on the Bonding Strength and Corrosion Resistance of Low-Pressure Cold Sprayed Al/Al2O3 Composite Coatings on Pressure Vessel Steel Substrate

Abstract

Due to the complex working environment, the defects were easily produced on the surface of pressure vessel plate, such as scratch, wear and corrosion pit, which reduced the service life of equipment. As a new surface coating preparation technology, cold spraying technology can be used to effectively repair and protect the substrate. With the development of cold spraying technology, more and more metal powders are used to prepare functional coatings, but aluminum powders are used most frequently due to significant plasticity and corrosion resistance. However, pure aluminum coating have a obvious shortcoming with lower bonding strength, and most of bonding strength values of coatings and steels are about 14.6 MPa. With the aim to improve the mechanical properties more of pure Al, the most representative one is the inclusion of ceramic particles as reinforcement to produce dense coatings. Thus, the Al-Al2O3 composite coatings of the different Al2O3 weight fractions were deposited on the surface of pressure vessel plate by cold spraying technology. The strength and corrosion resistance of the coatings were evaluated by tensile test, corrosion weight loss measurement and electrochemical test. The results show that the bonding strength of pure Al coating is the lowest among the four cold spray coatings, and the bonding strength sharply increases while the coating increased Al2O3 particles, and the largest values with bonding strength of Al-Al2O3 is as high as 45.4 MPa. The tensile test was carried out under the allowable stress of pressure vessel. Observations under optical microscope (OM) were also done, and the coating has excellent quality and no new cracks and holes. The corrosion weight-loss of the substrate and composite coatings were measured, and the corrosion weight loss rate of Al-Al2O3 was 5 times lower than that of pressure vessel plate. In addition, for all the coatings, the values of weight loss had little changes. It is observed that the values of the composite coating was exhibited a peak with an increasing of the Al2O3 content. The Al-20wt.%Al2O3 was shown the best corrosion resistance and the value of weight loss was 0.11(g/cm2*h), which probably was attributed to the effect of the lower porosity. Potentiodynamic polarization curves were shown the corrosion current density of composite coatings were one order of magnitude lower than that of the substrate. Therefore, we concluded that the corrosion resistance is obviously better than that of the substrate, which can effectively protect the substrate and delay the service life of the pressure vessel plate.