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通过透射电子显微镜(TEM)观察并结合纳米束能谱(EDS)分析,研究了Mg96.9Gd2.8Nd0.3(at%)合金在极限服役温度300℃等温时效状态下析出相的形成和生长。确定了300℃等温时效析出序列为:MgS.S.S.S→β1(fcc)→β(fcc),未见常规服役温度时效初期亚稳相β’’和β’。镁基体中均匀弥散的面心立方结构的亚稳相β1成分为Mg7RE,是300℃时效合金的主要析出强化相。合金在300℃具有更快的时效硬化效应,但显著的过时效效应导致合金力学性能迅速下降。
The formation and growth of precipitated phase of Mg96.9Gd2.8Nd0.3 (at%) alloy under isothermal aging at 300 ℃ were investigated by transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDS). The isothermal aging precipitation sequence at 300 ℃ was determined as follows: MgS.S.S.S → β1 (fcc) → β (fcc). The initial metastable phase β ’’ and β ’were not observed. The metastable phase β1 component of the uniformly dispersed face-centered cubic structure in the Mg matrix is Mg7RE, which is the main precipitation strengthening phase of the 300 ℃ aged alloy. The alloy has a faster aging hardening effect at 300 ℃, but the significant over-aging effect leads to the rapid decrease of the mechanical properties of the alloy.