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KFM: Fachverband Kristalline Festkörper und deren Mikrostruktur

KFM 24: Spectroscopy and Microscopy II with Positrons

KFM 24.1: Hauptvortrag

Donnerstag, 15. März 2018, 09:30–10:00, E 124

Discovering Ancient Secrets in Aluminum Alloys – A New Combination of Analytical Techniques and ab-initio Calculations — •Torsten E.M. Staab, Danny Petschke, Frank Lotter, and Elischa Bläss — LCTM, Universität Würzburg, Röntgenring 11, D-97070 Würzburg

Even though Aluminum alloy systems containing only two alloying elements seem to be just textbook example, there are still after decades of research unsolved problems in understanding the earliest stages of the formation of precipitates immediately after solution heat treatment and quenching. We tried to tackle these problems by a combination of different analytic method (DSC, XAFS, SAXS, PALS) combined with ab-initio calculations (SIESTA) of atomic configurations providing atomic positions for calculations of spectroscopic data and, thus, being able to directly compare our calculations to performed experiments.

For AlCu-alloys containing, on the one hand, Mg as a second alloying element we find that Mg-atoms are not catching quenched-in vacancies better than copper, as believe since long ago. However, the precipitation process seems to be triggered by large lattice distortions due to precipitation of Cu-platelets, where Mg atoms prefer lattice sites being under strain. On the other hand, we have been investigating the effect of trace elements in concentrations of 50 - 250ppm in 5N5 purity AlCu, where some of them (In, Sn) are known to bind quenched-in vacancies while other (Pb, Bi) – even larger in size – obviously do not have the same effect. The reason for this behavior is still under discussion.