(1. 南京工程学院 材料工程学院，南京 211167；
2. 南京航空航天大学 材料科学与技术学院，南京 210016)
摘 要: 交变载荷作用下在AZ31镁合金疲劳裂纹尖端渗注磷酸盐转化液，研究磷酸盐的沉积行为及其对AZ31镁合金疲劳裂纹扩展速率的影响。采用扫描电镜(SEM)、能谱仪(EDS)、X射线衍射仪(XRD)观察分析裂纹尖端的形貌和物相组成，并采用贴应变片方法确定渗注磷酸盐转化液前后应力强度因子的变化。结果表明：渗注的磷酸盐转化液在AZ31镁合金疲劳裂纹尖端形成Zn3(PO4)∙4H2O及MgZnP2O7复合覆层，能改变疲劳裂纹尖端的应力大小和分布状态，使应力强度因子降低约30%，从而有效地增强疲劳裂纹闭合效应，降低或延滞AZ31镁合金疲劳裂纹的扩展。
关键字: AZ31镁合金；磷酸盐；疲劳裂纹扩展；疲劳裂纹闭合
fatigue crack propagation in AZ31 magnesium alloy
（1. School of Material Engineering, Nanjing Institute of Technology, Nanjing 211167, China;
2. College of Material Science and Technology, Nanjing University of Aeronautics and Astronautics,
Nanjing 210016, China）
Abstract:Under alternate loads, a phosphate liquid was immersed into the fatigue crack tip of AZ31 magnesium alloy, the phosphate deposition behavior and effects of the phosphate film on the fatigue crack propagation rate at the fatigue crack tip of AZ31 magnesium alloy were investigated. The morphologies and phase constitutions of the phosphate deposition at the fatigue crack tip were characterized by scanning electron microscopy (SEM), energy spectrum analysis (EDS) and X-ray diffractometry (XRD), respectively. The stress-intensity factor values at the fatigue crack tip were compared with and without inmersing phosphate liquid by taking advantage of strain gauge. The results show that the phosphate( Zn3(PO4)∙4H2O and MgZnP2O7) films can be formed at the fatigue crack tip of AZ31 alloy through inmersing phosphate liquid, and the stress magnitude and distribution change after inmersing phosphate liquid at the fatigue crack tip of AZ31 alloy. The stress-intensity factor value decreases by about 30%, which effectively improves the fatigue crack closure, and reduces or arrearage the fatigue crack propagation.
Key words: AZ31 magnesium alloy; phosphate; fatigue crack propagation; fatigue crack closure
