Solute clustering and precipitation of Al-Cu-Mg-Ag based alloyTuesday (05.11.2019) 14:00 - 14:20 Part of:
The addition of micro-alloying elements (i.e. Ag) into Al-Cu-Mg based alloys can greatly improve the high temperature performance, which can be directly correlated to the different type solute clusters and precipitates formed during the aged treatment. However, these solute clusters and precipitates have not been systemically characterized. More importantly, there is a lack of the solute partitioning information into the precipitates. In this contribution, transmission electron microscopy (TEM) and atom probe tomography (APT) were employed to characterize the solute clustering and precipitates in Al-Cu-Mg-Ag based alloy. TEM characterizations and APT analyses reveal that, in as-quenched condition, four different solute clustering (co-cluster of Mg-Ag, Mg/Ag/Cu-rich cluster, Mg/Si-rich cluster and Cu-rich cluster) were observed. With increasing ageing time up to 1 h, a more significant solute clustering was observed. Furthermore, Ag significantly partitions into Mg/Ag-rich cluster and Mg/Ag/Cu-rich cluster and thereby results in the segregation of Mg and Cu and the formation of Mg/Ag-rich cluster and Mg/Ag/Cu-rich cluster. After ageing at 200 °C for 24 h, three different types of precipitates (Al-Cu (θ) phase, Al-Cu-Mg-Ag (Ω) phase and Mg-Si phase) were observed. Most Mg-Si phases are related to or located in the vicinity of Al-Cu phases. After ageing at 200 °C for 100 h, the same precipitates (Al-Cu (θ) phase, Al-Cu-Mg-Ag (Ω) phase and Mg-Si phase) were also observed. More interestingly, one Mg, Ag-rich layer was observed in the vicinity of Al-Cu (θ) phase, which was double confirmed by APT and high-angle annular dark-field (HAADF) imaging as well as electron energy loss spectroscopy (EELS) in scanning transmission electron microscope (STEM). These careful TEM characterizations and quantitative atom probe data analyses give us some hints to design novel Al alloy and optimize some important Al alloy in service.