(1. 湖南科技大学材料科学与工程学院，湘潭411201；
2. 西北工业大学材料学院，西安 710072；
3.北京航空材料研究院，北京 100095)
摘 要: 利用万能材料试验机、透射电子显微镜(TEM)和扫描电子显微镜(SEM)，研究了热暴露对7475-T761铝合金微观组织和力学性能的影响。结果表明：在100℃热暴露时，合金强度随着时间延长略有升高；在125℃热暴露时，合金强度随着时间延长略有降低，且力学性能在较长时间内保持稳定；当热暴露温度高于150℃时，合金强度随着时间延长急剧降低，伸长率快速升高。其主要原因是基体析出相(MPt)η′和η长大粗化、晶界析出相(GBP)η粗化以及晶界无析出带(PFZ)宽化。随着热暴露温度升高和时间延长，合金的断裂机制呈现由沿晶断裂和韧窝断裂组成的混合断裂转变为穿晶韧窝断裂。影响合金断裂行为的主要因素是基体与晶界之间的强度差异。
关键字: 7475铝合金；热暴露；微观组织；力学性能
（1. School of Materials Science and Engineering, Hunan University of Science and Technology, Xiangtan 411201, China;
2. School of Materials Science and Engineering, Northwestern Polytechnical University, Xi’an710072, China;
3. Beijing Institute of Aeronautical Materials, Beijing 100095, China）
Abstract:The effects of the thermal exposure on microstructure and mechanical properties of 7475-T761 Al alloy were studied by universal material testing machine, transmission electron microscopy (TEM) and scanning electron microscope (SEM). The results show that the strength of the alloy increases slightly when the alloy is exposed at 100℃. When the alloy is exposed at 125℃, the strength of the alloy decreases slightly and the mechanical properties remain stable for a long time. When the thermal exposure temperature is higher than 150℃, the alloy strength reduces sharply and the elongation increases rapidly with the prolongation of time.Coarsening of matrix precipitates(MPt), coarsening of grain boundary precipitates(GBP), and widening of precipitate free zones(PFZ) should be responsible for the strength decline and elongation rise of 7475-T761 Al alloy during thermal exposure.With increasing the temperature or prolonging the time, the fracture mechanism of the alloy gradually transforms frommixed fracture including intergranular fracture and dimple fracture to transgranular dimple fracture. The main factor that affect the fracture behavior of the alloy is the intensity difference between matrix and grain boundary.
Key words: 7475 Al alloy; thermal exposure; microstructure; mechanical property
