An analysis of Cu-content-driven quench sensitivity in aviation Al-Cu-Li alloys

Abstract

Quenching is a critical heat treatment for aging-hardenable Al-Cu-Li alloys. However, current research on the Cu-content-driven quenching precipitation behaviors remains limited. In this paper, the quench sensitivity of Al-Cu-Li alloys with a broad range of Cu contents (3.0 wt% ∼ 4.0 wt%) was detailed investigated through a serial of interrupted quenching treatments. Furthermore, the interaction between Cu atoms and vacancy was deeply analyzed based on the first principles calculation. Analysis of the constructed Time-Temperature-Transformation (TTT) and Time-Temperature-Property (TTP) curves reveals a decreased “nose tip” temperature and a shorter incubation period with the increase in Cu content. The increased Cu content accelerates the decomposition of supersaturated solid solution (SSSS), facilitating coarse Cu-rich particles precipitation during quenching process. This enhanced quenching precipitation is primarily attributed to the decreased formation energy and stronger binding energy of the Cu-Vacancy pairs for the sample with higher Cu content, which thereby lowers the nucleation and diffusion activation energy for quenching precipitates. Furthermore, the precipitation of Cu-rich particles leads to a reduction of the aging precipitates during the subsequent aging process, especially for θ’ phase. The quenching precipitation behavior also changes the subsequent aging precipitation sequence and promotes the formation of δ’ phase. This work aims to provide experimental and theoretical basis for the fabrication process and composition design of aviation Al-Cu-Li alloys with large scale thickness.