Precipitation Behavior in High‐Purity Aluminium Alloys with Trace Elements – The Role of Quenched‐in Vacancies

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. In dilute high purity aluminium alloys, the interaction of quenched‐in vacancies with specific trace elements is investigated by differential scanning calorimetry, positron annihilation lifetime spectroscopy, and scanning and transmission electron microscopy. The binding of vacancies to elements like In and Sn or Pb directly after quenching as well as during annealing of the alloys is shown.