利用扫描背散射电子像(SEM-BSE)和透射电子显微像(TEM)观察,研究了MgGd3,MgGd3Nd0.3和MgGd3Nd0.3Zn0.33种合金的铸态、固溶态显微组织结构,同时利用显微硬度仪研究了3种固溶态合金在200℃下的时效硬化行为.结果表明:3种合金经过520℃固溶处理后,均能使富稀土的初生相有效地固溶,形成可时效强化的过饱和固溶体合金.其200℃时效后峰值硬度的实现都源于基体中微细β’析出相的形成和弥散分布,而随后硬度随时效时间的变化趋势却有所不同.添加稀土元素Nd,有助于加快合金的时效响应.Nd和Gd共存时的析出强化使MgGd3Nd0.3合金在0～120 h时效阶段具有高于其他两种合金的硬度.过渡族元素Zn的添加,虽然使MgGd3Nd0.3Zn0.3的硬度相比MgGd3Nd0.3略低,但能够在长时间时效中保持硬度不明显下降.基于透射电镜观察,着重分析对比了在200 ℃ 85 h时效条件下的3种合金的显微结构特征,讨论了添加Nd和Zn元素对析出相尺寸、形貌和分布特征的影响.
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