中文摘要：

利用扫描电镜背散射电子像、透射电镜观察及能谱分析，研究了铸态MgGd1.8Y0.8Zn0.7（at．％）在400℃热处理前后结构的变化。结果发现，400qC热处理可导致铸态合金中初生Mg3Gd型第二相的部分分解及长周期堆垛结构（LPS）的形成。热处理形成的LPS结构为畸变的6H型，多存在于Mg3Cd型相及Mg5RE型相的前沿，并与较密集的堆垛层错（SV）组成一个富Zn元素的混合区——（SF＋LPS）区。Mg5RE型相存在于热处理后的合金中，具有fcc结构，与Mg基体有确定的取向关系，其与（SF＋Lps）区的相界处存在一个宽约10nm的过渡层。

英文摘要：

SEM-BSE, TEM observations and EDS analysis have been applied to investigate the as-cast and heat-treated microstructures of the MgGd3.0 Y0.8 Zn0.8s （at. % ）alloy. The results show that, heat treatment at 400℃ can result in decomposition of the as-cast primary phases of the Mg3Gd type, and this is responsible for the formation of a long period stacking structure （LPS）. The LPS belongs to a distorted 6H type and it can grow together with stacking faults （SF） of high density to form a SF ＋ LPS mixing region adjoining the Mg3 Gd- and Mg5 Gd-type phases. The Mg5Gd-type phase, observed in the heat-treated alloy, has a fcc structure and definite orientational relationship with the Mg matrix. There exists a transitional layer about 10 nm in width along its phase boundary with the SF ＋ LPS region.