Important progress has been made in grain refinement of magnesium-rare earth alloys

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

Magnesium-rare earth alloys have broad application prospects in aerospace and transportation fields because of their low density, high specific strength and specific stiffness, good heat resistance and excellent damping properties. Grain refinement can not only improve the strength and plasticity of mg-RE alloy, but also improve its casting properties, which is of great significance to promote the application of mg-RE alloy in aerospace and other key fields. At present, Mg-Zr master alloy is mainly used to refine magnesium-rare earth alloy in engineering practice. however, the agglomeration of Zr particles in commercial Mg-Zr master alloy is serious, and these Zr agglomeration is very easy to settle in magnesium melt, which not only greatly reduces the yield of Zr and the effect of grain refinement, but also produces serious refinement decline effect. Therefore, the study on the microstructure regulation of Mg-Zr master alloy to reveal the effect of the microstructure characteristics of the refiner on grain refinement and its decay effect has important theoretical and practical application value for the design and development of high efficiency magnesium rare earth alloy grain refiner.

In this study, Professor Wu Guohua's team creatively put forward a pretreatment method of grain refiner for Mg-Zr master alloy, which can significantly improve the microstructure uniformity and refinement effect of Zr grain refiner by ultra-high frequency pulse remelting. It is found that this pretreatment method can not only greatly increase the content of solute Zr in the grain refiner of Mg-Zr master alloy, but also promote the supersaturated precipitation of a large number of nanoscale (several nanometers to hundreds of nanometers) Zr particles, and significantly refine the Zr particle size of the refiner. Based on the microstructure heredity of Mg-Zr master alloy grain refiner, the microstructure evolution mechanism of Mg-Zr master alloy during pretreatment was revealed. Combined with the thermodynamic conditions of interfacial metallurgical reaction between matrix and nucleation core, the inhibition effect of nanometer Zr on crystal growth and the effect of heterogeneous nucleation in Mg-Zr master alloy were investigated, which put forward a new idea for the design and preparation of high efficiency grain refiner. The refinement experiments show that the pretreatment process proposed in this study can greatly improve the grain refinement effect of magnesium-rare earth alloys.

In recent years, Professor Wu Guohua's team has made a series of innovative research achievements in the development, preparation and molding of high-performance magnesium-rare earth alloys, which has made an important contribution to promoting the application of magnesium-rare earth alloys.