Investigation of Corrosion Resistance and Interfacial Bonding Properties of Zn/Zn–Al Multilayer Coating/Steel Substrate System

As an important mechanical property index, the interfacial bonding properties between coating and substrate are key factors in determining the corrosion resistance and reliability of the system. In this paper, the corrosion resistance performance and interfacial bonding properties of the Zn/Zn–Al multilayer coating/steel substrate system were studied. Neutral salt spray tests and electrochemical tests were conducted to evaluate the corrosion resistance of the coatings. Meanwhile, the three-point bending test with the acoustic emission (AE) technique was used to study the interfacial bonding properties of the multilayer coating/substrate systems. As a comparison, these tests were carried out on a Zn monolayer coating/substrate system and a Zn–Al monolayer coating/substrate system. The corrosion test results showed that the superposition of the Zn/Zn–Al coating/substrate system with different grain sizes hinders the transport path of corrosive ions, resulting in rust spots appearing later in the multilayer coating/substrate system than in the monolayer coating/substrate system. Given the increase in coating thickness, the defects, porosity, and corrosion through the holes of the coating increase, which aids in the corrosion process and reduces the corrosion resistance of the coating. The interfacial bonding strength of the system was analyzed using fracture toughness. The test results showed that the extent of the depreciation of the fracture toughness of the multilayer coating/substrate system before and after corrosion is lower than that of the monolayer coating/substrate systems. The interfacial bonding properties of the multilayer coating/substrate system are better than that of the monolayer coating/substrate systems because of the good material matching and dislocation effect between the multilayer coatings.