(1. 有研科技集團有限公司 國家有色金屬及電子材料分析測試中心，北京 100088；
2. 國標(北京)檢驗認證有限公司，北京 101407；
3. 北京有色金屬研究總院，北京 100088；
4. 國合通用測試評價認證股份公司，北京 101407；
5. 有研工程技術(shù)研究院有限公司 有色金屬材料制備加工國家重點實驗室，北京 101407)
摘 要: 采用聚焦離子束定點切割技術(shù)(Focused ion beam, FIB)，透射電鏡(Transmission electron microscopy, TEM)、高角度環(huán)形暗場掃描透射電鏡(High angle annular dark field scanning transmission electron microscopy, HAADF-STEM)和掃描電鏡(Scanning electron microscopy, SEM)等技術(shù)手段，對Mg-7Gd-5Y-1Nd-2Zn-0.5Zr合金鑄態(tài)及(515 ℃，48 h)均勻化態(tài)的組織形貌進行觀察分析。結(jié)果表明：鑄態(tài)合金晶界共晶組織中含有(Mg, ？Zn)3RE相(FCC, a=0.72 nm)、Mg5(RE, ？Zn)相(FCC, a=2.24 nm)及塊狀長周期堆垛有序(Long-period stacking ordered, LPSO)相。其中LPSO相主要為18R結(jié)構(gòu)，存在少量14H結(jié)構(gòu)，局部區(qū)域存在少量不完整周期的LPSO結(jié)構(gòu)；此外合金中存在分布于共晶相附近的微米級富RE相以及分布于晶粒內(nèi)部的微米級富Zr顆粒。經(jīng)過(515 ℃，48 h)均勻化熱處理，晶界(Mg, ？Zn)3RE相和Mg5(RE, Zn)相完全回溶，殘留相主要為14H-LPSO相，局部區(qū)域存在具有不同晶體結(jié)構(gòu)的LPSO過渡相。在鑄態(tài)合金的晶粒內(nèi)部，沿 晶帶軸觀察，發(fā)現(xiàn)存在幾個原子面至納米尺度的LPSO構(gòu)建塊，由不同數(shù)量的LPSO構(gòu)建塊單元(4個RE/Zn原子層)及Mg原子層交替堆垛構(gòu)成，RE/Zn與Mg原子層堆垛次序不具備完整周期性；均勻化熱處理后，晶內(nèi)的LPSO構(gòu)建塊幾乎回溶，僅剩下極少量單個LPSO構(gòu)建塊單元。沿 晶帶軸觀察，晶粒內(nèi)部存在多種分布方式的富RE/Zn原子柱，為Mg-Gd-Y系鎂合金時效過程β′析出序列中GP區(qū)的早期結(jié)構(gòu)。
關(guān)鍵字: 鎂合金；長周期堆垛有序結(jié)構(gòu)；高角度環(huán)形暗場像；LPSO構(gòu)建塊
（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
