均匀化退火后冷却条件对Al-Cu合金组织性能影响

为优化铝合金均匀化退火后的冷却工艺参数，采用动态电阻法、扫描电镜、透射电镜观察、能谱分析和硬度测试等方法，研究了均匀化处理后的冷却条件对Al-4%Cu合金组织性能的影响.获得的电阻率-温度曲线与材料的脱溶行为有良好的相关性.随着均匀化处理后冷却速率的降低，实验合金在冷却过程中会依次析出平衡相θ、亚稳相θ′和θ″.绘制了实验合金的CCT图，确定的脱溶敏感温度区间为500~300 ℃.选用合适的冷却工艺可以改善合金的组织性能，冷却时间超过1 000 min，合金有较低的硬度和电阻率.当实验合金均匀化后冷却至室温的时间处于19.4~184.1 min时会析出θ″相，导致硬度和电阻率上升，不利于后续的塑性加工，应该尽量避免.
In order to optimize the cooling parameters after homogenization, the microstructure and properties evolutions during the cooling processes have been investigated by in-situ electrical resistivity measurements, scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive spectrometer (EDS) and hardness test. The result has shown that the electrical resistivity curves have a good agreement with the precipitation behaviors. There were three types of precipitates in the studied alloy under different cooling conditions. And the precipitation sequence was equilibrium θ phase, metastable θ′ phase and θ″ phase. The hardness-time and resistivity-time curves revealed that choosing a suitable cooling condition could improve the microstructures and performance of the alloy. The optimal cooling time was exceeding 1 000 min, so that the hardness and resistivity of the alloy was located in a low level. However, the cooling should avoid being finished in the 19.4~184.1 min. The precipitation of θ″ phase in this range would lead to the increasing of hardness and resistivity, which was harmful to the subsequent plastic working.