Yang, Z.; Erdle, I.; Liu, C.; Banhart, J.: Clustering and precipitation in Al-Mg-Si alloys during linear heating. Journal of Materials Science & Technology 120 (2022), p. 78-88
10.1016/j.jmst.2021.11.062
Open Access Version
Abstract:
Differential scanning calorimetry (DSC) is a technique extensively applied to analyse precipitation phenomena in Al-Mg-Si alloys, yet the processes occurring during non-isothermal DSC heating, in particular the formation of clusters in the early stage and their evolution at higher temperatures, remain obscure. Here, we carry out experiments not only to measure heat (via DSC) but also to measure hardness, positron lifetime, electrical resistivity and microstructure of an Al-Mg-Si alloy heated at 3 different rates. Electrical resistivity is measured in situ, the other properties after interrupting the heating process. It is demonstrated that the precipitation process during heating can be divided into various stages, with transition temperatures depending on the heating rate, but the relative behavior of the various measured quantities is connected in the same way. Quenched-in excess vacancies are found to play an important role in cluster formation at lower temperatures, which explains the seeming peculiarity that linear heating at lower temperatures can lead to stronger clustering than isothermal ageing at a higher temperature. These trends are well simulated using a recently developed precipitation model. New aspects about the evolution of these clusters at higher temperatures are revealed by correlating the different measured properties. The methodology applied here could also be extended to investigating more complex non-isothermal heat treatments.