Zn含量对Mg-Gd-Nd-Zn合金中析出相 和长周期堆垛结构形成的影响

Effect of Zn Content on Formation of Precipitate Phases and Long-Period Stacking Strcture in Mg-Gd-Nd-Zn Alloys

摘要:

利用扫描电镜背散射电子技术、透射电子显微镜观察及能谱成分分析，研究在400 ℃时效处理过程中，不同Zn含量对铸态MgGd3Nd0.3Znx(x=0~1.25, at%，下同)系列合金中析出相和长周期堆垛（LPS）结构形成的影响。结果表明：在时效处理过程中，当Zn含量x≤0.62的合金中初生第二相附近的镁基体中析出平衡相β，而初生第二相则相对稳定无明显变化；当Zn含量x≥1.06时，合金镁基体中无β相析出，初生第二相开始瓦解，并在第二相与镁基体间形成一个含有高密度层错和LPS结构的富Zn和稀土元素的过渡区域。通过对不同Zn含量合金中第二相、过渡区以及镁基体中的成分对比分析，探讨高Zn含量Mg-Gd-Nd-Zn 合金中LPS结构的形成原因及生长过程。

Abstract:

SEM-BSE, TEM and EDS techniques were applied to investigate the effect of Zn content on formation of precipitate phases and long-period stacking structure in MgGd3Nd0.3Znx alloys (x=0-1.25, at%) during aging at 400 oC. The results show that the alloys with x≤0.62 precipitate equilibrium β-phases around the as-cast secondary phases which remain stable at 400 oC, while for those with x≥1.06, the precipitation of β-phases does not take place in the Mg matrix. In the high Zn-content alloys, the as-cast secondary phases are no longer stable; they turn to decompose, and this leads to the formation of Zn- and RE-rich transition regions containing both stacking faults of high density and LPS between those undecomposed secondary phases and Mg matrix. With the aid of the compositional analysis of secondary phases, transition regions and Mg matrix in heat-treated MgGd3Nd0.3Znx alloys, the formation reason and process of the LPS in the high Zn-content alloys were discussed.