Improvement of corrosion resistance of passivated magnesium powder metallurgical materials: repair mechanism of oxide film damage in Cl ⁻ environment

Passivation magnesium powder metallurgical materials have been widely used in many fields, but their corrosion resistance is facing severe challenges in environments containing Cl ⁻. Cl ⁻ has strong penetrability and can damage the oxide film on the surface of materials, leading to increased corrosion. Therefore, studying the repair mechanism of oxide film damage in Cl ⁻ environment is crucial for improving the corrosion resistance of the material.

In the Cl ⁻ environment, the damage to the oxide film is mainly caused by the adsorption and erosion of Cl ⁻. Cl ⁻ has a small radius and high charge density, making it easy to adsorb at defects on the surface of the oxide film, forming an acidic environment and accelerating the dissolution of the oxide film. At the same time, Cl ⁻ can also pass through the oxide film and react with the base metal to generate soluble chlorides, further damaging the integrity of the oxide film.

There are a series of repair mechanisms within the material itself to address the damage to the oxide film. Firstly, in the early stage of oxide film damage, the base metal will quickly react with oxygen in the surrounding environment, forming magnesium oxide again at the damaged area. Magnesium oxide has high chemical stability and can to some extent prevent further erosion by Cl ⁻. This self-healing process depends on the activity of the base metal and the oxygen content in the environment. When the oxygen concentration in the environment is high, the self-healing reaction rate accelerates, which can more effectively repair damaged oxide films.

Secondly, the alloying elements in the material also play an important role. Some alloying elements such as aluminum, zinc, etc. will preferentially react with Cl ⁻ when the oxide film is damaged, forming stable compounds. These compounds can fill the damaged area and form a protective film to prevent the deep penetration of Cl ⁻. For example, aluminum chloride generated by the reaction of aluminum element with Cl ⁻ can cover the damaged area to a certain extent, reducing the corrosion of Cl ⁻ on the base metal.

In addition, the microstructure of the material surface can also affect the repair of oxide films. Materials with a dense microstructure have a relatively small exposed area at the site of oxide film damage, which facilitates self-healing reactions. Meanwhile, the dense structure can also hinder the diffusion of Cl ⁻ to a certain extent, providing favorable conditions for the repair of oxide films.

In order to further improve the corrosion resistance of passivated magnesium powder metallurgical materials in Cl ⁻ environment, some auxiliary measures can be taken. For example, by using surface treatment technology to form a denser and more stable protective film on the material surface, it enhances its resistance to Cl ⁻. Alternatively, the alloy composition of the material can be optimized by adding alloying elements with good resistance to Cl ⁻ corrosion, in order to enhance the material's self-healing ability.

In depth research on the repair mechanism of oxide film damage in Cl ⁻ environment can help develop passivated magnesium powder metallurgical materials with better corrosion resistance and expand their applications in fields such as marine engineering and chemical engineering.