(1. 有研科技集团有限公司 有色金属材料制备加工国家重点实验室，北京 100088；
2. 有研工程技术研究院有限公司，北京 100088；
3. 北京有色金属研究总院，北京 100088)
摘 要: 以工业化挤压生产大截面尺寸的ZM51镁合金为研究对象，测试挤压态和T6态合金沿挤压方向(ED)的静态力学性能，并在应力比R=-1的条件下，研究T6态ED试样的高周疲劳行为。结果表明：T6处理后，ED试样的拉伸和压缩强度均得到提升，但伸长率大幅降低，压缩屈服强度的提高幅度远低于拉伸屈服强度的，合金拉压屈服不对称性增加。T6态ZM51镁合金循环周次为1×107时的疲劳极限为103 MPa，约为其抗拉强度的30%。发生在裂纹尖端塑性区内的“拉伸孪生-退孪生”是主要的疲劳损伤机制。合金疲劳裂纹的萌生位置以试样表面附近的孪晶界为主，疲劳裂纹穿晶路径扩展。疲劳断口两侧存在覆盖整个断口的针状孪晶层，应力越大，孪晶层厚度越小，而单个晶粒内的针状孪晶的数量越多，且间距越小。
关键字: 变形镁合金；拉压屈服不对称性；高周疲劳；孪生；退孪生
（1. State Key Laboratory of Nonferrous Metals and Processes, GRINM Group Co., Ltd., Beijing 100088, China;
2. GRIMAT Engineering Institute Co., Ltd., Beijing 100088, China;
3. General Research Institute for Non-ferrous Metals, Beijing 100088, China）
Abstract:The industrially extruded ZM51 magnesium alloy was studied in the present work. The static mechanical properties of as-extruded and T6 treated samples along extrusion direction (ED) were tested, and the high cycle fatigue behavior of T6 ED samples were studied under stress ratio R=-1. The results show that the tensile and compressive strength of the ED sample are improved by T6 heat treatment, but the elongation is greatly reduced, and the increment of the compressive yield strength is much lower than that of the tensile yield strength, resulting in the rise in the yield-strength asymmetry. The fatigue strength of T6 treated ZM51 alloy is 103 MPa under 1×107 cycle conditions, which is about 30% of its tensile strength. The tensile twinning and detwinning mechanism play a dominate role in fatigue deformation process, which is occurred in the plastic zone of the crack tip. The fatigue crack mainly initiates at the twin boundaries near the specimen surface, and propagates in a trans-granular mode. There are a large number of needle twins on both sides of the fatigue fracture which cover the whole fracture. The larger the stress, the larger the number of needle twins, and the smaller the spacing. The thickness of twin layer near the fracture decreases with the increase of the stress.
Key words: wrought magnesium alloy; tension-compression yield asymmetry; high cycle fatigue; twinning; detwinning
