均匀化退火后冷却条件对Al-Cu合金组织性能影响

Effect of cooling conditions after homogenization on the microstructure and performance of an Al-Cu alloy

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.