Softening Behavior During Annealing of Overaged and Cold-rolled Aluminum Alloy 7075

This work proposes studying the softening kinetics of aluminum alloy 7075-T6. Firstly, AA 7075 strips were overaged (300°C and 5 hours). Then, the overaged strips were cold-rolled at room temperature (45% in thickness reduction) and, after that, annealed at different temperatures (200°C and 250°C) and time intervals (30 minutes - 4 hours). By using polarized light microscopy, EBSD and Vickers hardness measurements, the softening mechanisms were determined and proper mathematical models (Kuhlmann, Johnson-Mehl-Avrami-Kolmogorov and Austin-Rickett) were used to analyse the experimental data. The results show that although almost all observed softening can be attributed to recovery, the phenomena is well described by using mathematical models for phase transformations (JMAK and Austin Riccket). In order to promote recrystallization of overaged AA 7075, an additional thickness reduction (75%) were used. These samples were annealed isocronically during 1 hour (100 - 400°C) and it was found that recrystallization only took place at 400°C.

本研究旨在探究7075-T6铝合金（aluminum alloy 7075-T6）的软化动力学行为。首先，将AA 7075铝合金带材进行过时效处理（300℃，保温5小时）。随后，将过时效后的带材在室温下进行冷轧，厚度压下率为45%；之后再于不同温度（200℃、250℃）及保温时长（30分钟至4小时）下开展退火处理。本研究采用偏光显微镜（polarized light microscopy）、电子背散射衍射（EBSD）以及维氏硬度测试手段，明确了软化机制，并选用适配的数学模型——库尔曼模型（Kuhlmann）、约翰逊-梅尔-阿夫拉米-科洛莫戈罗夫模型（Johnson-Mehl-Avrami-Kolmogorov，简称JMAK）以及奥斯汀-里基特模型（Austin-Rickett）——对实验数据进行分析。结果表明，尽管观测到的软化现象几乎全部可归因于回复过程，但采用相变类数学模型（JMAK模型与奥斯汀-里基特模型）可对该现象进行精准拟合。为促进过时效AA 7075铝合金的再结晶，本研究采用了额外的冷轧工艺，厚度压下率达75%。将该组试样在100℃至400℃的温度区间内进行等时退火，保温时长均为1小时，结果发现仅在400℃时发生了再结晶。