In situ heating TEM observations of evolving nanoscale Al-Mg-Si-Cu precipitates

This research concerns the precipitation and subsequent dissolution of precipitate phases in an Al-0.86Mg-0.62Si-0.1Cu (at.%) alloy subjected to varying thermal exposure during an in situ heating transmission electron microscope (TEM) experiment. The distribution and crystal structure of precipitates were determined by a scanning diffraction approach at multiple stages, pinpointing the precipitates that underwent phase transformations during heating. Obtained results were compared with TEM studies of the material heated ex situ. This revealed differences in the transformation kinetics of precipitates in an electron transparent lamella (thickness $$ ) to that of macroscopic bulk specimens. LAY DESCRIPTION: The precipitate phases that are formed in age-hardenable Al alloys are conventionally studied using the TEM, with electron transparent specimens prepared from bulk materials heat treated for various times. We demonstrate here that the growth, phase transformation and subsequent dissolution of precipitate phases in the Al-Mg-Si-Cu system can be studied successfully by in situ heating TEM. Imaging and scanning diffraction combined with data postprocessing were used to study the distribution and structure of transforming precipitates. This enabled us to track the precipitates that underwent phase transformations during heating, hence offering a direct quantitative assessment of the precipitation occurring in these materials. The narrow thickness of the electron transparent specimen (≈90 nm) may potentially have affected the resulting precipitation. Therefore, thickness effects were assessed by comparing obtained results with TEM studies of ex situ heated bulk specimens.