(1. 中南大学 材料科学与工程学院，长沙 410083；
2. 中南大学 有色金属材料科学与工程教育部重点实验室，长沙 410083)
摘 要: 采用疲劳强度及裂纹扩展测试、扫描电镜和电子背散射衍射等方法研究难溶结晶相分布特征对7020铝合金型材疲劳行为的影响。结果表明：合金中直径小于2 μm的难溶结晶相占比较大，且数量较多；当直径大于4 μm的难溶结晶相较少时，疲劳强度可达113.3 MPa，比含较多大尺寸难溶结晶相的合金疲劳强度高16.4%。当应力强度因子ΔK=10 MPa·m1/2时，含较多大尺寸难溶结晶相比含密集且细小的合金裂纹扩展速率快21.0%。直径在3~17 μm的粗大难溶结晶相在疲劳循环中因自身开裂或与基体界面脱粘而易形成裂纹源，其中直径在3~7 μm之间的难溶结晶相加速疲劳裂纹扩展的频率最高。尺寸细小的难溶结晶相能均匀分散应力，增加裂纹断面粗糙度，提高合金疲劳性能。难溶结晶相也能影响合金再结晶程度和晶界特征，再结晶分数和大角度晶界降低时可以提高疲劳裂纹扩展抗力。
关键字: 7020铝合金；难溶结晶相；疲劳强度；疲劳裂纹扩展
（1. School of Materials Science and Engineering, Central South University, Changsha 410083, China;
2. Key Laboratory of Nonferrous Metal Materials Science and Engineering, Ministry of Education, Central South University, Changsha 410083, China）
Abstract:The influence of intermetallic particles on fatigue behavior of 7020 aluminum alloy profile was investigated by fatigue strength test, fatigue crack growth test, scanning electron microscopy and electron back scattering diffraction technique. The results show that the fatigue strength of the alloy containing amounts of intermetallic particles with a diameter of less than 2 μm and few particles with a size of greater than 4 μm reaches 113.3 MPa, which is 16.4% higher than that of the alloy with more large-sized intermetallic particles. The fatigue crack growth rate of the alloy containing more large-size intermetallic particles is 21.0% faster than that of the alloy with dense and fine intermetallic particles. The coarse intermetallic particles with a diameter of 3 to 17 μm are likely to form fatigue crack initiation due to self-cracking or debonding from the substrate during fatigue cycles. And the particles with a diameter between 3 and 7 μm have the highest frequency of accelerating fatigue crack growth. The intermetallic particles with small size can evenly distribute stress, increase the roughness of the crack section, and improve the fatigue performance of the alloy. The intermetallic particles also affect the recrystallization fraction and grain boundary characteristics of the alloy. When the recrystallization fraction and high angle grain boundary of the alloy are reduced, fatigue crack propagation resistance can be improved.
Key words: 7020 aluminum alloy; intermetallic particle; fatigue strength; fatigue crack growth
