Research Progress Magnesium Alloys

1. Heat-resistant magnesium alloy

Poor heat resistance is one of the main reasons that hinder the widespread application of magnesium alloys. When the temperature rises, its strength and creep resistance drop significantly, making it difficult to be used as a key part (such as engine parts) material in automobiles and other industries. Get more widely used. The alloying elements used in the developed heat-resistant magnesium alloys are mainly rare earth elements (RE) and silicon (Si). Rare earth is an important element used to improve the heat resistance of magnesium alloys. Rare earth-containing magnesium alloys QE22 and WE54 have high-temperature strength comparable to aluminum alloys, but the high cost of rare earth alloys is a major obstacle to their wide application.
Mg-Al-Si (AS) series alloy is a die-cast magnesium alloy developed by German Volkswagen. At 175 cC, the creep strength of AS41 alloy is significantly higher than that of AZ91 and AM60 alloys. However, AS magnesium alloys will form coarse Chinese-character-like Mg2Si phases during solidification, which impairs casting performance and mechanical properties. Studies have found that the addition of trace Ca can improve the morphology of the Chinese-character MgaSi phase, refine the Mg2Si particles, and improve the structure and properties of the AS series magnesium alloys.、

2. Corrosion resistant magnesium alloy

The corrosion resistance of magnesium alloys can be solved in two ways:
1) Strictly limit the content of impurity elements such as Pe, Cu and Ni in the magnesium alloy. For example, the corrosion resistance of high-purity AZ91HP magnesium alloy in the salt spray test is about 100 times that of AZ91C, which exceeds the die-cast aluminum alloy A380, and is much better than low carbon steel.
2) Surface treatment of magnesium alloy. According to different corrosion resistance requirements, chemical surface treatment, anodic oxidation treatment, organic coating, electroplating, chemical plating, thermal spraying and other methods can be selected. For example, the corrosion resistance of electroless magnesium alloy exceeds that of stainless steel.

3. Flame retardant magnesium alloy

Magnesium alloys are prone to violent oxidation and combustion during the melting and casting process. Practice has proved that the flux protection method is an effective flame-retardant method, but they will cause serious environmental pollution in their application, and reduce the performance of the alloy and increase the equipment investment.
The addition of calcium to pure magnesium can greatly improve the oxidation and combustion resistance of the magnesium liquid, but the addition of a large amount of calcium will seriously deteriorate the mechanical properties of the magnesium alloy, making this method unable to be used in production practice.
Recently, the National Engineering Research Center of Light Alloy Precision Forming of Shanghai Jiaotong University has developed a flame-retardant magnesium alloy for passenger cars with good flame-retardant and mechanical properties by adding several elements at the same time, and successfully carried out the automobile gearbox cover Industrial testing and production of electronic product shells such as mobile phone shells and MP3 shells.

4. High strength and toughness magnesium alloy

The normal temperature strength and plastic toughness of existing magnesium alloys need to be further improved. The addition of Ca and Zr to Mg-Zn and Mg-Y alloys can significantly refine the grains and improve their tensile strength and yield strength; adding Ag and Th can improve the mechanical properties of Mg-RE-Zr alloys, such as containing Ag QE22A alloy has high room temperature tensile properties and creep resistance, and has been widely used as high-quality castings for aircraft and missiles; through rapid solidification powder metallurgy, high extrusion ratio and equal channel angular extrusion (ECAE) methods, magnesium The grains of the alloy are processed very finely to obtain high strength, high plasticity and even superplasticity.