Aging Behavior of Mg-Y-Zr and Mg-Nd-Zr Cast Alloys

Aging behavior of Mg-3.6Y-0.5Zr and Mg-2.TNd-0.5Zr alloys was investigated by microhardness measurement and transmission electron microscopy.In the case of Mg-Y-Zr alloy,the presence ofβ″phase,a major strength- ener,having base centered orthorhombic structure with its lattice constants of a-（β″）=0.64 nm,b-（β″）=2.22 nm, and c-（β″）=0.52 nm was identified.In the case of Mg-Nd-Zr alloy aged at 250℃,the presence ofβ″andβ′phases was identified.The crystal structure ofβ″phase was found to be DO-（19） and its orientation relationships with Mg matrix were [0001]-（β″）//[0001]-（Mg） and [01（？）0]-（β″）//[01（？）0]-（Mg）.Theβ′phase had face centered cubic structure and its orientation relationships with Mg matrix were [011]-（β′）//[0001]-（Mg） and [（？）1（？）]β′//[（？）110]）-（Mg）. The Mg-2.TNd-0.5Zr alloy showed higher hardness compared with Mg-3.6Y-0.5Zr alloy.

Texture development and grain boundary phase formation in Ce-and Ce-La-substituted Nd-Fe-B magnets during hot-deformation process

In this study,the influence of Ce-and Ce-La-substitution for Nd in Nd-Fe-B magnets on their magnetic and microstructural changes in the course of the hot-deformation process was investigated to gain insight into further reducing the Nd content in fine-grained Nd-Fe-B hot-deformed magnets.We found that the[001]texture and microstructure of the RE-rich grain boundary phases,which are the factors that de-termine the remanence and coercivity of hot-deformed magnets,were deteriorated by the Ce-and Ce-La-substitution.This is because the volume fraction of the RE-rich liquid formed in the grain boundaries during the hot-press and hot-deformation decreased due to the Ce-and Ce-La-substitution,thereby in-creasing the friction between the 2:14:1 grains while the c-axes of grains were aligned by grain rotation and decreasing the RE concentration of grain boundary phases.In particular,the Ce-La-co-substitution further prevented the liquid formation within the grain boundaries of the magnets during hot-press and hot-deformation because the wettability of the RE-rich liquid on the 2:14:1 grains became poor when La was substituted for Nd in the 2:14:1 grains.These results indicate that there is room for further im-provement in both the remanence and coercivity of the Ce-and Ce-La-substituted magnets by intro-ducing additional liquid into the grain boundaries prior to hot-press and hot-deformation.By applying the Nd-Cu infiltration process to the melt-spun ribbons(intermediate infiltration,I-infiltration),both the remanence and coercivity of the Nd-saving(Nd 0.7 Ce 0.3)-Fe-B and(Nd 0.7 Ce 0.225 La 0.075)-Fe-B hot-deformed magnets were successfully improved.