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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“C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”C 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。
The as-cast and solid solution microstructures of MgGd3, MgGd3Nd0.3 and MgGd3Nd0.3Zn0.33 alloys were investigated by scanning electron microscopy (SEM-BSE) and transmission electron microscopy (TEM) The age hardening behavior of three solid solution alloys at 200 ℃ was studied by using microhardness tester. The results show that all of the three alloys can effectively dissolve the rare earth-rich primary phase after solution treatment at 520 ℃, forming supersaturated solid solution alloy with aging strengthening effect. The results show that the peak hardness after aging is derived from the formation and dispersion of the fine β ’precipitates in the matrix, and then the trend of hardness changes with the aging time is different.Add rare earth element Nd, help to speed up The aging response of the alloy.The precipitation hardening of the coexistence of Nd and Gd makes the hardness of the MgGd3Nd0.3 alloy higher than that of the other two alloys at 0-120 h aging stage.The addition of Zn as a transitional group element makes the MgGd3Nd0.3Zn0.3 Its hardness is slightly lower than that of MgGd3Nd0.3, but its hardness can not be obviously decreased after long time aging.Based on the transmission electron microscope observation, the microstructural characteristics of three alloys under 200 ℃ aging conditions are analyzed and compared. The effects of Nd and Zn addition on the size, morphology and distribution of precipitates were discussed.