2元系マグネシウム合金の粒界偏析計算と底面集合組織および室温成形性との関係調査

抄録

Amounts of segregation at grain boundaries of Mg-0.05at％X (X = Al, Bi, Ca, Ce, Gd, Nd, Y, Zn, Zr) alloys were calculated by using the Hillert’s grain boundary phase model. As a result, relatively high grain boundary segregation was obtained in each case of Ca, Ce, Nd, Y and Zn. In addition, the basal plane texture and Erichsen value of the alloys were experimentally investigated, which exhibits a similar tendency to the previous experiments, i.e., the Erichsen value decreases with decreasing basal texture intensity. High-angle annular dark-field STEM (HAADF-STEM) analysis of the Mg-0.4Nd (mass％) and Mg-0.2Y (mass％) sheets elucidated that the uniform grain boundary segregation was detected in Mg-0.4Nd, while the localized and scattered segregation region was observed at grain boundary in Mg-0.2Y. These segregation behaviors were explained by the concept of critical element concentration proposed by Griffiths. An un-recrystallized grain microstructure with high lattice distortion was observed in Mg-0.4Nd in Scanning Electron Microscope - Electron Back-Scatter Diffraction (SEM-EBSD) analysis, which leads to a possibility that the grain boundary segregation of Nd contributes to the suppression of recrystallization during rolling. As the strong correlation was observed between the calculated grain boundary segregation and the experimental basal texture intensity, the amount of grain boundary segregation is a useful parameter for describing basal texture intensity of binary Mg alloys.

Fig. (a) Relationship between inverse of basal texture intensity and calculated atomic fraction of various elements in grain boundary of Mg, (b) Relationship between index Erichsen value and calculated atomic fraction of various elements in grain boundary of Mg.