(1. 兰州理工大学省部共建有色金属先进加工与再利用国家重点实验室，兰州 730050；
2. 兰州理工大学材料科学与工程学院，兰州 730050；
3. 兰石铸造有限公司，兰州 730050)
摘 要: 采用光学显微镜(OM)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)、X射线衍射仪(XRD)、维氏硬度计和万能试验机，研究了挤压和时效态Mg-6.8Y-2.5Cu(质量分数，%)合金的显微组织和力学性能。结果表明：挤压合金主要由α-Mg基体、沿挤压方向分布的片层状和块状18R类型的长周期堆垛有序相(18R-LPSO)、Mg2Cu相以及晶粒内细小条纹状的14H-LPSO相组成。180 ℃等温时效后，亚稳18R-LPSO相分解，晶内析出新的14H-LPSO相。合金在58 h和130 h处分别出现两个硬度峰值，其硬度值分别为69.2 HV和70.2 HV。第一个时效峰的出现主要源于大量18R-LPSO相和部分14H-LPSO相的析出。第二个时效峰的出现源于晶粒内部高体积分数14H-LPSO相的析出。拉伸测试结果表明：时效130 h的挤压合金在室温下具有最高的极限抗拉强度(276.8 MPa)和伸长率(25.9%)。合金高的抗拉强度主要归因于14H-LPSO相的析出强化及18R-LPSO相的弥散强化。
关键字: 挤压Mg-Y-Cu合金；LPSO相；显微组织；力学性能
（1. State Key Laboratory of Advanced Processing and Recycling of
Nonferrous Metals,Lanzhou University of Technology, Lanzhou 730050, China;
2. School of Materials Science and Engineering,
Lanzhou University of Technology, Lanzhou 730050, China;
3. Lanshi Foundry Co., Ltd., Lanzhou 730050, China）
Abstract:The microstructure and mechanical properties of the extruded and aged Mg-6.8Y-2.5Cu alloys were investigated by optical microscope (OM), scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray diffractometer (XRD), Vickers micro-hardness tester and tensile testing machine. The results show that the extruded alloy is mainly composed of α-Mg matrix, lamellar and block 18R type long-period stacking ordered (18R-LPSO) phase distributes along the extrusion direction, Mg2Cu phase and the fine striped 14H-LPSO phase in the grain interior. During the 180 ℃ isothermal aging process, parts of metastable 18R-LPSO phases occurrs to dissolve and the new 14H-LPSO phase precipitated in Mg matrix. Two hardness peaks of the extruded alloy appear at 58 h and 130 h, and hardness values are 69.2 HV and 70.2 HV, respectively. The first ageing peak arises from a great number of 18R-LPSO phases and small amounts of 14H-LPSO phases. The second aging peak originates from the precipitation of a large number of 14H-LPSO phases in the grain interior. The tensile test results show that the extruded alloy aged for 130 h exhibits the highest ultimate tensile strength (276.8 MPa) and elongation (25.9%) at room temperature. The good tensile strengths of the alloy are mainly attributed to the precipitation strengthening of the 14H-LPSO phase and the dispersion strengthening of the 18R-LPSO phase.
Key words: extruded Mg-Y-Cu alloy; LPSO phase; microstructure; mechanical property
