Nano-scaled early stage Si or Mg containing clusters in Al-Mg-Si alloys are experimentally extremely difficult to observe and atom probe tomography (APT) is the only technique to visualize and chemically measure these clusters today. Two examples for the technological importance of understanding clustering during natural aging in the Al-Mg-Si system are presented. First, a quenching procedure is shown to significantly alter the overall excess-vacancy concentration consequently altering solute clustering kinetics. Second, trace element additions are shown to trap excess-vacancies and hence to reduce the freely available vacancy concentration, which results in decreased solute clustering. The modification and understanding of early stage clustering is commercially important since it has strong implications on the strength evolution during industrial heat treatments. However, restrictions remain in achieving the ultimate quantification of such small solute aggregates by APT. Especially the surface migration of Si atoms is an open issue. However, an accurate adjustment of measurement and analysis parameters is known to minimize this problem. Nevertheless, clustering directly after quenching has not been possible to investigate because of the time required for sample preparation and sample transfer into the analysis chamber. Here we present a new strategy how the measurement of as-quenched conditions and very early stages of natural aging can be realized via APT. This can be accomplished via sample production at cryogenic temperatures to suppress diffusion. The shown procedure includes cryogenic focused ion beam (FIB) preparation and direct cryogenic transfer of fresh APT samples into the analysis chamber of an atom probe. Results on as-quenched and in-situ naturally aged Al-Mg-Si alloys are presented. Furthermore, the effect of FIB induced clustering at cryogenic temperatures is discussed.
To cite this abstract:Stefan Pogatscher, Phillip Dumitraschkewitz, Stephan S.A. Gerstl; Atom probe tomography of early stage clustering in Al alloys. The 16th European Microscopy Congress, Lyon, France. https://emc-proceedings.com/abstract/atom-probe-tomography-of-early-stage-clustering-in-al-alloys/. Accessed: March 21, 2019
EMC Abstracts - https://emc-proceedings.com/abstract/atom-probe-tomography-of-early-stage-clustering-in-al-alloys/