The corrosion of magnesium and its alloys has greatly limited the application of magnesium alloys in practical engineering for a long time. It is an important task to develop appropriate protective measures and make them withstand the "test" in specific environment.

⒉ Factors affecting the corrosion properties of Magnesium Alloy

The alloy composition and impurity elements in magnesium alloys have significant influence on the corrosion resistance of magnesium alloys. Harmful impurity elements, such as Fe, Ni, Cu and so on, must be strictly controlled during magnesium alloy smelting. Fe cannot be solidly dissolved in magnesium matrix and can only be distributed in the grain boundary in a free state, which reduces the corrosion resistance of magnesium alloy. When Fe content is greater than 0.016mass%, the corrosion rate of magnesium alloy increases sharply. The microstructure also affects the corrosion resistance of magnesium alloys. Magnesium alloys have different corrosion behaviors in different corrosive media. In humid environment, magnesium alloy corrosion is accelerated with the increase of humidity.

3. Basic types of magnesium alloy corrosion

The corrosion types of magnesium and magnesium alloys include total corrosion, galvanic corrosion, high temperature oxidation, pitting corrosion, crevice corrosion, intergranular corrosion, stress corrosion cracking and corrosion fatigue. Among them, galvanic corrosion, stress corrosion cracking and corrosion fatigue are common and harmful corrosion types in application of magnesium alloys.

4. Corrosion protection of magnesium alloys

The corrosion of magnesium alloy can be prevented by avoiding direct contact with corrosive medium, which is mainly through magnesium alloy surface modification and surface coating. Surface modification mainly includes chemical conversion treatment, electroplating and electroless plating, anodic oxidation and micro-arc oxidation, laser surface treatment and so on. The surface coating includes metal coating, organic coating and special coating.

Microarc oxidation is considered as one of the most promising surface treatments for magnesium alloys. The ceramic oxide film can be formed in situ on the magnesium alloy surface. The ceramic film can greatly improve the hardness, wear resistance, corrosion resistance and electrical insulation properties of the magnesium alloy surface. The surface treatment method has the characteristics of simple process, high treatment efficiency, no pollution and so on, which meets the development requirements of current cleaning industry.