(1. 国网湖南省电力有限公司 电力科学研究院，长沙 411107 2. 中南大学 材料科学与工程学院，长沙 410083； 3. 国网湖南电力有限公司 湘电试验研究院有限公司，长沙 410004)
摘 要: 采用扫描电镜和透射电镜观察、电阻率和硬度测试等手段，研究连续冷却条件对7020合金时效组织性能的影响，并绘制实验合金的CCT图。结果表明：实验合金的连续冷却脱溶产物主要包括GP区、η′相和η相，高温阶段主要对应η相在弥散粒子、晶界等异质形核质点上的优先析出，中温阶段主要对应η相在基体内均匀析出，低温阶段则主要对应GP区、η′相的析出，实验合金的临界冷却速率达到700 ℃/min以上。不同冷却条件引起析出相组态的变化，导致合金的硬度和电阻率随冷却速率降低而发生相应的变化。较慢冷却速度下的脱溶会消耗溶质原子，从而导致时效驱动力下降，而合适的冷却速率下形成的亚稳相则可作为时效强化相的前驱体，能够加速时效强化相析出，导致合金的时效硬化曲线峰值时间提前。
关键字: 7020合金；连续冷却；显微组织；CCT图
（1. Electrical Power Research Institute, State Grid Hunan Electrical Power Company, Changsha 411107, China; 2. School of Materials Science and Engineering, Central South University, Changsha 410083, China; 3. Hunan Xiangdian Test Research Institute Co. Ltd., State Grid Hunan Electrical Power Company, Changsha 410004, China）
Abstract:The effect of continuous cooling process on aging microstructure and properties was investigated by means of scanning electron microscopy (SEM), transmission electron microscopy (TEM), electrical resistivity and hardness test. The results show that the continuous cooling precipitations for 7020 alloy are GP zones, η and η′ phases. The high temperature transformation corresponds to the heterogeneous precipitation of η phase. The medium temperature zone corresponds to the homogeneous precipitation of η phase. While, GP zones and η′ phases are precipitated in the low temperature zones. The critical cooling rate for 7020 alloy inhibiting any cooling precipitates is more than 700 ℃/min. The hardness and electrical resistivity change with the extending of cooling ending time with the extending of cooling ending time, since the different microstructures induce by different cooling processes. The precipitation of metastable phases during the cooling process leaded to an earlier peak hardness value is observed. However, extremely slow cooling processes will lead to the significant consumption of alloy atoms, in which the driving force for aging precipitation decreases.
Key words: 7020 alloy; continuous cooling; microstructure; CCT diagram
