Statistical and Thermodynamic Optimization of Trace-Element Modified Al-Mg-Si-Cu Alloys

Al-Mg-Si-Cu alloys exhibit natural aging, which negatively influences artificial aging. Additions of trace elements have been recently shown to eliminate this effect: At room temperature quenched-in vacancies are trapped by trace solutes in the ppm range and natural aging is supressed, while at higher temperatures these vacancies are released and artificial aging is promoted. In this study we determine an optimum in chemical composition and solution heat treatment temperature for Sn and In-doped Al-Mg-Si-Cu alloys. Automated thermodynamic calculations coupled with a statistical evaluation of influencing parameters on solubility of Mg, Si, Cu, Sn and In were used to find maximum strengthening potential and dissolved trace element content. Theoretical predictions are compared to aging experiments. The method enables detailed and rapid analysis of a wide compositional and temperature space in multicomponent systems.