Grain Refinement and Second Phases Evolution of Mg-13Gd-4Y-2Zn-0.4Zr Sheet During Processing by Rotary Forward Extrusion

다국어 초록 (Multilingual Abstract)

The grain refinement and second phases evolution of Mg-13Gd-4Y-2Zn-0.4Zr sheet during the rotary forward extrusion(RFE) process were investigated. The microstructures were observed by using optical microscopy, scanning electron microscopy,electron backscatter diffraction, X-ray diffractometer, and transmission electron microscope. The result shows, the modifiedcellular automata model fully considers the influence of long-period stacking ordered phase on the dislocation density,which can predict the grain size evolution of Mg-Gd-Y-Zn-Zr alloy during the RFE process, and the relative error can becontrolled within 10%. With the increase of RFE revolutions, the average grain size firstly decreases quickly (RFE1–RFE25),and then increased gradually (RFE25–RFE100). The decreased grain size is related to the enhanced dynamic recrystallizationprocess as the c-axis of most grains is rotated continuously to a transverse direction and more random texture types areformed. The increase in grain size is linked with the solid solution of the second phase, and the limitation on grain growthdue to the pinning effect of the second phase almost disappears. In the early stage (RFE1–RFE25), the contribution percentageof grain refinement and solid solution strengthening to microhardness improvement is 180.6% and 61.7%, respectively.
In the subsequent stage (RFE25–RFE100), the dislocation density strengthening and solid solution strengthening accountsfor 60% and 440% of the increase in microhardness, respectively.