Corrosion protection method of magnesium alloy

The corrosion of magnesium alloys has greatly limited the application of magnesium alloys in practical engineering for a long time. Develop appropriate protective measures to withstand the specific environment “ Test ” It is an important task to expand the application of magnesium alloy and its products.

1. Basic characteristics of magnesium alloy corrosion

The standard electrode potential of magnesium is -2.37V, 1.93V lower than iron and 0.66V lower than aluminum, and the electrode potential of magnesium in ordinary media is also very low. The oxide of magnesium is loose and porous, and the oxide layer obtained by magnesium oxidation cannot protect the aluminum substrate like alumina, so the magnesium alloy is easy to corrode.

2. Factors affecting corrosion performance of magnesium alloy

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

3. Basic types of magnesium alloy corrosion

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 harmful corrosion types in magnesium alloy applications.

4. Magnesium alloy anti-corrosion

Avoiding direct contact between magnesium alloys and corrosive media can prevent corrosion of magnesium alloys, mainly through surface modification and surface coating of magnesium alloys. The surface modification mainly includes chemical conversion treatment, electroplating and electroless plating, anodic oxidation and micro-arc oxidation, laser surface treatment and so on. Surface coatings include metal coatings, organic coatings and special coatings.

Micro arc oxidation is considered as one of the most promising surface treatment methods for magnesium alloys. It can form a ceramic oxide film on magnesium alloy surface in situ, which can greatly improve the hardness, wear resistance, corrosion resistance and electrical insulation properties of magnesium alloy surface. The surface treatment method has the characteristics of simple process, high treatment efficiency and no pollution, which meets the development requirements of current clean industry.