In this work, the influence of the Cu content on the solidification microstructure, precipitation microstructure and hardness was investigated firstly. Subsequently, the influence of the separate or combined addition of 0.7 wt.% Ag and 0.3 wt.% Mg on the same parameters was considered. Finally, the targeted alloy Al-4Cu-0.3Mg-0.7Ag was investigated under following conditions: (i) after hot rolling up to six different plate thicknesses at 250 °C and in the rolling state, (ii) after T4 solution treatment at 540 °C for 6 hours, and (iii) ageing at 170 °C for 12 hours. The observation of the microstructure was carried out with the use of the optical microscope for the build-up alloys after a Barker etching and under the SEM for the Al-4Cu-0.3Mg-0.7Ag alloy and the rolled respective samples. Hardness of the T4 treated samples after natural aged for seven days was determined according to Vickers. The the precipitation behaviour was investigated using small angle X-ray scattering (SAXS) at 170 °C and DSC, respectively.
It was found that with increasing Cu content the hardness increases, the formation of a significant amount of precipitates starts with a content of 4 wt.% Cu. The addition of 0.3 wt.% Mg into an Al-4Cu alloy leads to an increase in hardness and postpones the formation of GP zones at 170 °C in SAXS to a later stage. The addition of 0.7 wt.% Ag to an Al-4Cu alloy results in an increased hardness and an increase in the precipitation density and coarsening. The hardness measurement of Al-4Cu-0.3Mg-0.7Ag alloy shows the highest values and the Ω-phase formed coarsens firstly and then shows an excellent thermal stability in the considered period of 40 hours. The hardness of the samples after rolling are below the original alloy regardless of the subsequent treatment. The Porod radius of the rolled specimens hardly changes, but the precipitation density shows slight differences. This master thesis provides a fundamental understanding of the influence of alloying elements (Cu, Mg, Ag) and hot rolling on the solidification microstructure, precipitation microstructure and hardness in Al-Cu-Mg-Ag alloy system, which is of great help for the further alloy development.