添加稀土Er于熔剂中对铸态AZ91镁合金组织与性能的影响

研究了熔炼时在熔剂(42%MnCl2 53%LiCl 5?F2,质量分数,%)中添加稀土Er对铸态AZ91镁合金显微组织、力学性能、断口形貌以及腐蚀行为的影响。结果表明:在熔剂中添加稀土Er能够去除镁合金熔炼过程中产生的熔剂夹杂,净化镁合金熔体,提高铸态AZ91镁合金的拉伸性能和耐腐蚀性能;当熔剂中添加10%的稀土Er时,镁合金的抗拉强度σb和伸长率δ分别从156MPa和1.8%上升到最大值220MPa和4.1%;同时,镁合金在5%NaCl水溶液中的腐蚀速率从1.20mg/(cm2.d)下降到最小值0.15mg/(cm2.d);然而,随着稀土Er在熔剂中添加量的进一步提高,合金中开始有φ-(Al7ErMn5)和τ-(Al66.7Mg23.3Er10)等含有稀土Er的相生成,消耗了合金中的Al和Mn元素,改变了β-(Mg17Al12)相的形态;而且沿枝晶界附近分布的粗大φ-(Al7ErMn5)相降低了枝晶之间的结合力,使得合金的σb和δ下降;同时,部分网状的β-(Mg17Al12)相断裂,呈离散的块状,导致合金的腐蚀速率增加;熔剂中添加稀土Er不改变镁合金的断裂机理,断裂机制仍为准解理断裂。     

Effect of erbium on microstructure and thermal compressing flow behavior of Mg-6Zn-0.5Zr alloy

A series of thermal compressing tests of Mg-6Zn-0.5Zr and Mg-6Zn-0.5Zr-1Er alloys were performed on a Gleeble-1500D thermal simulator. The microstructures of thermal compressed Mg-6Zn-0.5Zr and Mg-6Zn-0.5Zr-1Er alloys were determined by optical microscopy, transmission electron microscopy and X-ray diffractometry. The results show that Mg-6Zn-0.5Zr alloy mainly consists of α-Mg and MgZn2 phase, while Mg-6Zn-0.5Zr-1Er alloy comprises α-Mg phase, coarse Mg3ZnnEr2 eutectic, rod-liked Mg3Zn4Er2 precipitated phase, fine I phase particle （Mg3Zn6Er, icosahedral quasicrystal structure）. The peak flow stress becomes larger with increasing strain rate and erbium addition at the same temperature, and gets smaller with increasing deformation temperature at the same strain rate. The deformation activation energy increases with increasing temperature, strain rate and erbium addition. In addition, it is observed that the growth of dynamic recrystallization （DRX） grains of Mg-6Zn-0.5Zr-lEr alloy was markedly suppressed due to the pinning effect of fine I phase and Mg3Zn4Er2 phase during thermal compression.     

镁合金LPSO/SFs结构间■孪晶交汇机制的原子尺度研究

以含长周期堆垛有序(LPSO)结构的Mg-Zn-Y(-Zr)合金为研究对象，运用透射电子显微方法，从原子尺度解析LPSO结构/富含溶质元素堆垛层错(SFs)对■孪晶交汇行为的作用。结果表明：LPSO/SFs与孪晶交截处易形成基面-棱柱面，从而引起孪晶界在LPSO/SFs间弯曲成弓形，孪晶界存在Zn元素偏聚，Y元素偏聚不明显。LPSO/SFs间同轴■孪晶变体交汇，引入基面-基面(BB)界面及柱面-柱面(PP)界面，且在近LPSO/SFs处产生三角形的局部基体结构。LPSO结构形成扭折时，■孪晶在扭折界面单侧形核长大，此处扭折界面转为孪晶界面；残余扭折界面与基体侧孪晶扩展界面相交，在LPSO/SFs近邻处形成三角形的基体结构。LPSO/SFs/TSFs (孪晶层错)间不同孪晶变体形核，以及交汇引入的分割带来的Hall-Petch效应，可提升合金的硬化率。通过调控镁合金LPSO结构的间距和厚度引入不同孪晶变体，可为其优化性能提供新思路。