Atom Probe Tomography Investigations of Modi ed Early Stage Clustering in Si-Containing Aluminum Alloys

In this paper atom probe tomography is used to explore early stage clustering in aluminum alloys. Two novel concepts for a modi cation of clustering are discussed. Control of early stage clustering is welcome from an application point of view since clustering deteriorates strength evolution during the industrial heat treatment of the important class of Al Mg Si precipitation-hardenable alloys. Nanoscale early stage clusters are very di cult to observe and atom probe tomography is the best technique to visualize and chemically measure Si or Mg-containing clusters in aluminum alloys. Restrictions remain in achieving the ultimate quanti cation of such small solute aggregates by atom probe tomography, such as detection e ciency, local magni cation e ects, surface migration of solute atoms, and unresolved issues with the reconstruction procedure. Here we investigate one of these restricting e ects, namely the migration of solute atoms during atom probe tomography measurements. In particular Si is found to be preferentially localized or absent at certain crystallographic poles in aluminum, which derogates the experimental results gained from atom probe tomography studies of clustering in Si-containing aluminum alloys. This artifact is investigated for di erent specimen temperatures, detection rates and pulse fractions during atom probe tomography measurements. Optimal strategies to analyze small-scale solute clusters in Si-containing aluminum alloys are presented.