Corrosion and Protection of Magnesium and Magnesium Alloys
The corrosion problem of magnesium and magnesium alloys has long greatly limited their application in practical engineering. Developing effective protective measures and enabling them to withstand the "test" in specific environments is an important issue in expanding the application of magnesium alloys and their 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 commonly used media is also very low. The oxide of magnesium is loose and porous, and the oxide layer obtained from magnesium oxidation cannot provide a certain protective effect on the aluminum substrate like alumina, so magnesium alloys are prone to corrosion.
2. Factors affecting the corrosion performance of magnesium alloys
The alloy composition and impurity elements in magnesium alloys have significant effects on the corrosion resistance of magnesium alloys. Harmful impurity elements, such as Fe, Ni, Cu and other elements, must be strictly controlled during magnesium alloy smelting. Fe cannot be solidly dissolved in the magnesium matrix and can only be distributed in a free state at the interface, thereby reducing the corrosion resistance of magnesium alloys. When Fe
When the content is greater than 0.016 mass%, the corrosion rate of magnesium alloy increases sharply. The microstructure of magnesium alloys also affects their corrosion resistance. Magnesium alloys exhibit different corrosion behaviors in different corrosive media. In a humid environment, magnesium alloy corrosion accelerates as humidity increases.
3. Basic types of corrosion of magnesium alloys
The corrosion types of magnesium and magnesium alloys include comprehensive corrosion, galvanic corrosion, high-temperature oxidation, pitting, 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 magnesium alloy applications.
4. Corrosion protection of magnesium alloys
Avoiding direct contact between magnesium alloys and corrosive media can prevent corrosion of magnesium alloys, mainly through surface modification and coating of magnesium alloys. Surface modification mainly includes chemical conversion treatment, electroplating and electroless plating, anodic oxidation and Plasma electrolytic oxidation, laser surface treatment, etc. Surface coatings include metal coatings, organic coatings, and special coatings Etc. Micro induced oxidation is considered one of the most promising surface treatment methods for magnesium alloys. It can form ceramic oxide film in situ on the surface of magnesium alloy, and the Ceramic membrane can
Greatly improve the surface hardness, wear resistance, corrosion resistance, and electrical insulation performance of magnesium alloys. This surface treatment method has simple process and treatment efficiency High, pollution-free and other characteristics, in line with the current development requirements of clean industry.
