Berlin 2018 – scientific programme

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KFM: Fachverband Kristalline Festkörper und deren Mikrostruktur

KFM 24: Spectroscopy and Microscopy II with Positrons

KFM 24.3: Talk

Thursday, March 15, 2018, 10:20–10:40, E 124

An atomic investigation of the clustering on a Friction-Stir-Welding simulated Al-Cu-Li(-Mg) alloy by Positron Annihilation, SAXS, XAFS and DSC — •Danny Petschke, Frank Lotter, and Torsten Staab — University Würzburg, Dep. of Chemistry, Röntgenring 11, D-97070 Würzburg

Al-Cu-Li(-Mg) alloys find wide applications in aviation and aerospace technology due to the reduction of weight and their high strength at the same time. After rolling sheets of these alloys, a defined heat treatment leads to the formation of mainly T1-precipitates. These precipitates are highly efficient in blocking dislocations. When these sheets are joined by Friction-Stir-Welding (FSW), temperatures occuring in the Weld-Nugget (WN) are close to the material's solution treatment temperature. Hence, the T1-precipitates are completely dissolved in this region, which results in a significant hardness-drop. Only sub-nanometer sized GP(B)-zones and CuMg-clusters are formed directly after welding by diffusion processes not understood in detail, yet. We followed the precipitation directly after welding with Differential Scanning Calorimetry (DSC), giving information on formed precipitates, Small Angle X-ray Scattering (SAXS), giving information on size and volume fraction, Positron Annihilation Lifetime Spectroscopy (PALS), being sensitive to the formation and growth of precipitates, and, X-ray absorption spectroscopy (XAFS) as a fingerprint-method to identify the atomic structure by comparing the experimentally obtained spectra to simulations. Therefore, a Welding-Simulator was developed to reproduce the temperature in the welded material.