Compared with other metals, the chemical properties of magnesium are more active. Magnesium in the molten state oxidizes and burns violently in the air. It easily reacts with oxygen, nitrogen, and water in the liquid state, and the corrosion resistance of magnesium and magnesium alloys. It is very sensitive to impurity elements such as Fe, Ni "Cu, etc. Therefore, in the process of melting magnesium alloy must be effective to prevent the oxidation or combustion of molten metal, otherwise it will not only reduce the quality of the melt which ring alloy purity, composition uniformity and accuracy , er, increase material loss and even danger.
The affinity between magnesium and oxygen is greater than the affinity of aluminum and oxygen, and a loose oxide film is formed on the surface of magnesium oxide. This oxide film cannot prevent the oxidation reaction. Instead, the heat generated at the reaction interface does not rapidly spread outward, resulting in The temperature rise at the interface accelerates the oxidation of magnesium.
Magnesium can also react with water. When molten magnesium comes into contact with water, not only does the magnesium oxide generate a large amount of heat, but the reaction product hydrogen reacts rapidly with oxygen in the surrounding atmosphere to generate water, which rapidly vaporizes and expands due to heat, resulting in violent The explosion caused intense combustion and splashing of the magnesium melt. Therefore, when the magnesium alloy is smelted, the charge, the tool, the flux, and the like that are in contact with the molten liquid should be dried.
The product of Mg and N2 reacting with nitrogen is a powdery compound and cannot stop the reaction from proceeding. At the same time, the Mg3N2 film cannot prevent the evaporation of magnesium, so N2 cannot prevent oxidation combustion of the magnesium melt.
Inert gases such as nitrogen, helium, and neon cannot react chemically with magnesium and prevent the combustion of magnesium melt. However, in these atmospheres, the magnesium melt cannot produce a protective surface film and therefore cannot prevent the evaporation of magnesium, which has a higher vapor pressure above the melting point.
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