Important Progress in Grain Refinement of Magnesium Rare Earth Alloys>

Recently, the team of Professor Guohua Wu from the National Engineering Research Center of Light Alloy Precision Forming of Shanghai Jiao Tong University and the team of Professor David H. StJohn from the University of Queensland in Australia have made important research progress in the grain refinement of magnesium rare earth alloys.

Magnesium rare earth alloys have low density, high specific strength and stiffness, good heat resistance, and excellent damping and vibration reduction, and have broad application prospects in aerospace and transportation fields. Grain refinement can simultaneously improve the strength and plasticity of magnesium rare earth alloys, and can also improve its casting process performance, which is of great significance for promoting the application of this alloy in key fields such as aerospace. At present, Mg-Zr master alloys are mainly used in engineering practice to refine magnesium rare earth alloys. However, the Zr particles in commercial Mg-Zr master alloys are seriously agglomerated, and these Zr agglomerations are easy to settle in the magnesium melt, which not only greatly reduces the Zr yield and grain refinement effect will also produce severe refinement recession effect. Therefore, the research on the microstructure control of Mg-Zr master alloys was carried out to reveal the effect of the microstructure characteristics of the refiner on the grain refining effect and its recession effect. Important theoretical and practical application value.

In this study, Professor Wu Guohua's team innovatively proposed a pretreatment method of grain refiner for Mg-Zr master alloys. Microstructure uniformity and refining effect of Zr grain refiner. The study found that this pretreatment method can not only greatly increase the content of solute Zr in the Mg-Zr master alloy grain refiner, but also promote the supersaturated precipitation of a large number of nano-scale (several nanometers to hundreds of nanometers) Zr particles, which is significantly finer. The Zr particle size of the refiner is reduced. Based on the microstructure heritability of grain refiners in Mg-Zr master alloys, the microstructure evolution mechanism of Mg-Zr master alloys during pretreatment is revealed. The inhibitory effect of nanoscale Zr on crystal growth and the influence of heterogeneous nucleation in Mg-Zr master alloys provide new ideas for the design and preparation of high-efficiency grain refiners. Refinement experiments show that the pretreatment process proposed in this study greatly improves the grain refinement effect of magnesium rare earth alloys.