Magnesium and magnesium alloys are highly reactive during the smelting process, which can lead to gas adsorption and oxidation inclusions, ultimately degrading the quality of the alloy. Additionally, their limited corrosion resistance and high-temperature creep performance restrict their application in certain areas. Rare earth elements, with their unique electron configuration and physical/chemical properties, have a stronger affinity for hydrogen and oxygen than magnesium itself. Their oxides also have higher density compared to magnesium oxide, making them excellent alloying agents. When added during the smelting of magnesium alloys, rare earth elements not only help remove hydrogen and reduce oxide inclusions but also refine the microstructure, enhance high-temperature performance, and improve overall mechanical properties.
This paper explores the mechanisms and applications of rare earth elements in magnesium alloys, focusing on purification, flame retardancy, microstructure refinement, improved high-temperature performance, and enhanced corrosion resistance.
**1. Purification of Magnesium Alloy Melt by Rare Earth**
**1.1 Hydrogen Removal**
Magnesium is highly reactive, especially with water vapor, leading to hydrogen evolution that results in porosity and defects in castings. Rare earth elements can effectively bind with hydrogen, forming high-melting-point hydrides and oxides that float to the surface as slag, removing hydrogen from the melt. The reaction equation is:
3H₂O(g) + 5[RE] → 3REH₂ + RE₂O₃
Thermodynamic calculations show that this reaction has a strong driving force, making rare earth elements effective in eliminating hydrogen and oxygen during the smelting process.
**1.2 Removal of Oxide Inclusions**
Magnesium readily reacts with oxygen to form MgO, creating inclusions that weaken the alloy's mechanical and corrosion resistance. Rare earth elements, with a greater affinity for oxygen than magnesium, can react with MgO to form stable rare earth oxides, reducing the number and size of inclusions. Studies have shown that adding rare earth elements can significantly reduce the volume fraction of inclusions in recycled magnesium alloys.
In addition to hydrogen and oxygen, rare earth elements can also interact with sulfur, nitrogen, and halogens, forming compounds that remove non-metallic impurities. At high temperatures, they react with carbon, silicon, and boron to form carbides, silicides, and borides, further improving the purity of the alloy.
**2. Flame Retardant Effect of Rare Earth**
During melting and casting, magnesium reacts with oxygen, forming MgO and releasing heat. However, the porous nature of MgO allows continued oxidation and combustion. Adding rare earth elements enhances the ignition point of magnesium alloys by forming dense oxide films composed of MgO, Al₂O₃, and RE₂O₃. These films prevent oxygen from reaching the melt, thus reducing the risk of combustion.
Studies have shown that adding rare earth elements such as cerium increases the light-off temperature of magnesium alloys, significantly improving their flame resistance. However, excessive rare earth content may lead to thick oxide layers that crack, reducing the flame resistance.
**3. Effect of Rare Earth on Microstructure of Magnesium Alloy**
**3.1 Influence on As-Cast Microstructure**
Rare earth elements form needle-like or strip-like phases with aluminum, which tend to segregate at grain boundaries, hindering grain growth and refining the microstructure. This leads to a more uniform distribution of intermetallic phases and improves the mechanical properties of the alloy.
**3.2 Effect on Solid Solution and Aging Treatment**
During solid solution treatment, rare earth elements form stable phases that reduce atomic diffusion, delaying age hardening. This can improve thermal stability and maintain mechanical properties at elevated temperatures.
**4. Impact of Rare Earth on Mechanical Properties**
Rare earth elements enhance the mechanical properties of magnesium alloys through grain refinement, solid solution strengthening, and grain boundary strengthening. They improve both room temperature and high-temperature strength, as well as creep resistance. For example, Mg-Y-Nd-Zr alloys exhibit excellent creep resistance at 300°C.
**5. Effect of Rare Earth on Corrosion Resistance**
Rare earth elements modify the corrosion layer structure of magnesium alloys, forming protective oxide films that resist corrosion. They also control cathodic phases, reducing the active area and improving electrochemical behavior. Studies have shown that adding rare earth elements like Ce significantly reduces the corrosion rate of AZ91 magnesium alloy.
**Conclusion**
China possesses abundant magnesium and rare earth resources, providing a unique advantage in developing rare earth-enhanced magnesium alloys. By leveraging the unique properties of rare earth elements, the performance of magnesium alloys can be further improved, especially in high-temperature and high-strength applications. This will expand their use in automotive, aerospace, and electronics industries, meeting the growing demand for high-quality, high-performance materials.
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Label: Rare Earth Magnesium Alloy
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Concerned about surprises
Label: Rare Earth Magnesium Alloy
Previous: Paying attention to the new progress of agricultural rare earth
Next: Application of rare earth in hot dip galvanizingRegulating valve is a fluid control device, it can control fluid flow, pressure, temperature and other parameters, in order to achieve the purpose of regulating fluid flow characteristics. It is composed of a piston or ball spool, in which there is a manual or electric mechanism with adjustment function, it can control the position of the piston or ball spool, so as to change the pressure and flow rate in the valve, so as to adjust the flow characteristics of the fluid.
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