Effect of Zr Addition on the Grain Refinement Mechanism of Mg-Gd-Er Alloys

In recent years, Zr is widely used as an important additive element in magnesium alloys containing rare earth (RE), to improve the mechanical properties of Mg-RE alloys such as strength, ductility, creep resistance and corrosion resistance property. Heterogeneous nucleation mechanism and peritectic reaction mechanism are recognized as the main grain refining mechanisms. Whereas, during the solidification process, the melt wetting angle and nucleation energy are important factors which influence the nucleation. In this work, the effect of Zr on the solidification microstructure of the Mg-Gd-Er alloy was analyzed by using OM and EBSD; the undercooling of alloy melts was tested by using DSC; and the Mg/Zr interface relationship and interfacial energy were investigated by using HRTEM. Moreover, the effects of Zr on the wetting angle and nucleation activation energy of the Mg-11Gd-2Er and Mg-11Gd-2Er-0.4Zr alloys were investigated; the refinement mechanism of Zr on the alloys was discussed. The results indicates that the addition of Zr element can significantly refine the grain, and the grain size decreased from 1000 μm to 50 μm. Compared with the Zr-free alloy, the nucleation wetting angle of the present alloy melt decreased from 18.3° to 11.1°, and the activation energy of nucleation decreased by 44.4%. The (1010) plane of Mg was completely coherent with the (1100) plane of Zr, reducing the interfacial energy between the (1010)Mg and the (1100)Zr. The grain refinement of Mg-Gd-Er alloy was ascribed to the decrease of melt wetting angle and the fully coherent interface relationship between Mg and Zr.

Duke Scholars

Author Zhaohui Wang Pathology