The Influence of Trace Elements (In, Sn) on the Hardening Process of Al-Cu Alloys

Adding trace elements (Cd, In, Sn) to Al-Cu-based alloys can significantly improve their strength by the growth of small and finely distributed precipitates. However, the underlying atomic mechanisms of their nucleation are so far only superficially understood. We follow the precipitation process, that is changes in the microstructure, by different methods: differential scanning calorimetry (DSC), giving information on formation and dissolution of precipitates, 3D atom probe tomography (3DAP), giving information on size and density of precipitates and finally, positron annihilation lifetime spectroscopy (PALS), being sensitive especially to quenched-in vacancies and their interaction with alloying elements. By the use of these complementary methods we obtain information on vacancy binding to the alloying elements and also on structure, kind and distribution of precipitates while correlating this with hardness measurements.