(1. 有研科技集团有限公司 国家有色金属及电子材料分析测试中心，北京 100088；
2. 国标(北京)检验认证有限公司，北京 101407；
3. 北京有色金属研究总院，北京 100088；
4. 国合通用测试评价认证股份公司，北京 101407；
5. 有研工程技术研究院有限公司 有色金属材料制备加工国家重点实验室，北京 101407)
摘 要: 采用聚焦离子束定点切割技术(Focused ion beam, FIB)，透射电镜(Transmission electron microscopy, TEM)、高角度环形暗场扫描透射电镜(High angle annular dark field scanning transmission electron microscopy, HAADF-STEM)和扫描电镜(Scanning electron microscopy, SEM)等技术手段，对Mg-7Gd-5Y-1Nd-2Zn-0.5Zr合金铸态及(515 ℃，48 h)均匀化态的组织形貌进行观察分析。结果表明：铸态合金晶界共晶组织中含有(Mg, ？Zn)3RE相(FCC, a=0.72 nm)、Mg5(RE, ？Zn)相(FCC, a=2.24 nm)及块状长周期堆垛有序(Long-period stacking ordered, LPSO)相。其中LPSO相主要为18R结构，存在少量14H结构，局部区域存在少量不完整周期的LPSO结构；此外合金中存在分布于共晶相附近的微米级富RE相以及分布于晶粒内部的微米级富Zr颗粒。经过(515 ℃，48 h)均匀化热处理，晶界(Mg, ？Zn)3RE相和Mg5(RE, Zn)相完全回溶，残留相主要为14H-LPSO相，局部区域存在具有不同晶体结构的LPSO过渡相。在铸态合金的晶粒内部，沿 晶带轴观察，发现存在几个原子面至纳米尺度的LPSO构建块，由不同数量的LPSO构建块单元(4个RE/Zn原子层)及Mg原子层交替堆垛构成，RE/Zn与Mg原子层堆垛次序不具备完整周期性；均匀化热处理后，晶内的LPSO构建块几乎回溶，仅剩下极少量单个LPSO构建块单元。沿 晶带轴观察，晶粒内部存在多种分布方式的富RE/Zn原子柱，为Mg-Gd-Y系镁合金时效过程β′析出序列中GP区的早期结构。
关键字: 镁合金；长周期堆垛有序结构；高角度环形暗场像；LPSO构建块
（1. National Center of Analysis and Testing for Nonferrous Metals and Electronic Materials, GRINM Group Co., Ltd, Beijing 100088, China;
2. Guobiao (Beijing) Testing & Certification Co., Ltd., Beijing 101407, China;
3. Beijing General Research Institute for Nonferrous Metals, Beijing 100088, China;
4. China United Test and Certification Co., Ltd., Beijing 101407, China;
5. State Key Laboratory of Nonferrous Metals and Processes, GRIMAT Engineering Institute Co., Ltd., Beijing 101407）
Abstract:The microstructure and the second phase of Mg-7Gd-5Y-1Nd-2Zn-0.5Zr alloy in as-cast and (515 ℃, 48 h) homogenized state were observed and analyzed by using focused ion beam(FIB) preparation technology, transmission electron microscopy(TEM), high-angle-annular-dark-field scanning transmission electron microscopy (HAADF-STEM), scanning electron microscopy(SEM) and other technical means. The results show that grain boundary eutectic phase of the as-cast alloy consists of (Mg, Zn)3RE phase (FCC, a=0.72 nm), Mg5(RE, Zn) phase (FCC, a=2.24 nm) and bulk long-period stacking ordered(LPSO) phase. The bulk LPSO phase is mainly 18R structure with a small amount of 14H structure and incomplete period LPSO structure in local position. In addition, there are micron RE-rich phases distributed near the eutectic phase and micron-scale Zr-rich particles distributed inside the grains. After homogenization treatment at (515 ℃, 48 h), (Mg, Zn？)3RE phase and Mg5(RE, Zn) phase are completely dissolved. The bulk LPSO phase is mainly 14H structure with transition LPSO phases of different crystal structures. Inside the grains of the as-cast alloy, observed along , it is found that there are several atomic layers to nano-scale LPSO building blocks, consisting of different numbers of LPSO building block units (4 RE/Zn atomic layers) and Mg atoms layer alternate stacking structure. The stacking sequence of RE/Zn and Mg atomic layers does not have a complete periodicity. After homogenization treatment, the LPSO building blocks inside the grain are almost dissolved, only a very small number of individual LPSO building block units remaining. There are multiple distribution modes of RE/Zn-rich atoms in the crystal grains observed along the , which are the early structures of the GP zone in the β′ precipitation sequence of the Mg-Gd-Y magnesium alloy aging process.
Key words: Mg alloys; long-period stacking ordered structures; HAADF-STEM; LPSO building blocks
