急冷凝固Ｍｇ９７Ｚｎ１ＲＥ２合金の微細組織観察

Abstract

The microstructure of ternary Mg97Zn1RE2 (RE=La, Ce, Gd, Tb, Dy, Ho or Er) melt-spun alloys annealed at 573 K for 1.2 ks have been investigated in order to clarify the relationship between their microstructures and hardness. The Mg97Zn1RE2 alloys consisted of Mg grains with diameter ranging from 0.7 to 2 μm. Also, several Mg–Zn–RE ternary phases were observed inside Mg grain and at grain boundary. Long period stacking (LPS) structure characterized as 14H-type was formed inside some Mg grains in the Mg97Zn1RE2 (RE=Gd, Tb, Dy, Ho or Er) alloys, respectively. The growth of 14H-type LPS structure from another Mg–Zn–RE ternary phase at grain boundary was recognized in the Mg97Zn1RE2 (RE=Gd or Er) alloys, and also the electron diffraction pattern clearly indicated that the relationship between 14H-type LPS structure and 2H-Mg was (001)2H–Mg // (0014)14H–Mg, indicating the 14H– and 2H–Mg were coexisted in the identical grain with certain relationship. On the other hands, although the LPS structure was not observed in the Mg97Zn1RE2 (RE=La or Ce) alloys, a number of the Mg–Zn–RE (RE=La or Ce) ternary phases with less than 50 nm dispersed in the Mg matrix, respectively. The higher hardness of the Mg97Zn1RE2 (RE=La or Ce) alloys than the Mg97Zn1RE2 (RE=Gd, Tb, Dy, Ho or Er) alloys originated in the formation of the numerous nano-size Mg–Zn–RE (RE=La or Ce) phases dispersed interior Mg grains in the Mg97Zn1RE2 (RE=La or Ce) alloys.