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Precipitation Behavior in High-Purity Aluminium Alloys with Trace Elements

The Role of Quenched‐in Vacancies
: Lotter, F.; Muehle, U.; Elsayed, M.; Ibrahim, A.M.; Schubert, T.; Krause-Rehberg, R.; Kieback, B.; Staab, T.E.M.


Physica status solidi. A 215 (2018), Nr.24, Art. 1800375, 11 S.
ISSN: 0031-8965
ISSN: 1862-6300
ISSN: 1521-396X
ISSN: 1862-6319
Fraunhofer IFAM, Institutsteil Pulvermetallurgie und Verbundwerkstoffe Dresden ()

The main mechanism for the strengthening of aluminium‐copper alloys of the 2xxx type is hardening by copper‐rich precipitates. However, their size, distribution, and crystal structure determine the final mechanical properties of the material. It has been shown that alloying additionally small amounts of cadmium, indium, or tin influences the precipitation behavior as well as the final strength of Al‐Cu alloys. The binding energy of quenched‐in vacancies to trace elements in the aluminium matrix is recognized as an influence on the diffusion behavior of the copper atoms and thus the preferred type of precipitate changes. A precondition for this influence is the transition of trace elements into solid solution during the solution heat treatment. In the present work, solubility and interaction with quenched‐in vacancies is analyzed for the elements In, Sn, Sb, Bi, and Pb in high‐purity binary alloys using differential scanning calorimetry (DSC), positron annihilation lifetime spectroscopy (PALS) as well as scanning and transmission electron microscopy (SEM, TEM). The results confirm on one hand literature data and deliver on the other hand new structural details. A subsequent anneal at moderate temperature leads to finely distributed precipitations on the nanoscale.