(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；
3. 包头职业技术学院，包头 014030；
4. 中南大学 轻质高强结构材料国家重点实验室，长沙 410083；
5. 河南省紧固连接技术重点实验室，信阳 464000)
摘 要: 采用Kahn撕裂实验，结合金相、扫描电镜、扫描透射电镜、数字图像相关法和电子背散射衍射等手段，研究了Cu含量对Al-9.0Zn-1.5Mg-xCu合金断裂韧性的影响规律。结果表明：随着Cu含量从0%增大到2.6%(质量分数)，合金断裂韧性先逐渐增大，在Cu含量为1.0%~1.3%时达到最高值，而后大幅减小。随着Cu含量从0%增大到1.0%~1.3%，合金的再结晶晶粒面积分数逐渐增大，导致裂纹形核过程的变形量和穿过再结晶晶粒扩展的比例增大；裂纹单位面积形核功(UIE)和单位面积扩展功(UPE)逐渐增大。Cu含量为2.6%时，合金残余第二相的面积分数、晶界上部分η相的尺寸增大，导致裂纹形核过程的变形量减小；η′强化相的间距减小，导致晶内-晶界强度差和裂纹沿再结晶晶界扩展的比例明显增大；UIE和UPE均大幅减小。
关键字: Al-Zn-Mg-Cu合金；Cu含量；断裂韧性；裂纹形核功；裂纹扩展功
（1. School of Materials Science and Engineering, Central South University, Changsha 410083, China;
2. Key Laboratory of Non-ferrous Metals Materials Science and Engineering, Ministry of Education, Central South University, Changsha 410083, China;
3. Baotou Vocational & Technical College, Baotou 014030, China;
4. National Key Laboratory of Light and High Strength Structural Materials, Central South University, Changsha 410083, China;
5. Henan Key Laboratory of Fastening Connection Technology, Xinyang 464000, China）
Abstract:The effect of Cu content on the fracture toughness of Al-9.0Zn-1.5Mg-xCu alloys was investigated by means of Kahn-tear test, optical microscopy (OM), scanning electron microscopy (SEM), scanning transmission electron microscopy (STEM), digital image correlation (DIC), and electron backscattered diffractionometry (EBSD). With the increase of Cu content from 0% to 2.6% (mass fraction), the fracture toughness of alloys first increases, reaching the maximum value at 1.0%-1.3%, and then decreases greatly. With the increase of Cu content from 0% to 1.0%-1.3%, the area fraction of recrystallized grains increases gradually, leading to an increase in the deformation amount during crack initiation and the proportion of transgranular fracture; therefore, unit initiation energy (UIE) and unit propagation energy (UPE) increase gradually. When Cu content is 2.6%, the area fraction of residual phase increases and there are some large η phase particles at grain boundaries, leading to a decrease in deformation amount during crack initiation; the spacing of η′ strengthening precipitates decreases, leading to an increase in the strength difference between the grain interior and the grain boundary and therefore higher proportion of intergranular fracture. As a result, UIE and UPE decrease greatly.
Key words: Al-Zn-Mg-Cu alloy; Cu content; fracture toughness; unit initiation energy; unit propagation energy
