Influence of the degree of scandium supersaturation on the precipitation kinetics of rapidly solidified Al-Mg-Sc-Zr alloys

In this work, we present for the first time detailed and quantitative precipitation kinetics of industry-scale belt-casted AlMg4Sc0.4Zr0.12 alloys. We investigate the age hardening behavior in a temperature range between 250 °C and 400 °C within 180 min as a function of the degree of scandium supersaturation prior to ageing. The hardness evolution is correlated to in-situ synchrotron X-ray diffraction measurements and the precipitate population is analyzed using high-resolution scanning transmission electron microscopy (HR-STEM) and energy filtered TEM in terms of precipitate size, volume fraction, and number density. Here we found that a greater solute Sc-content results in more pronounced age hardening and slightly faster Al3(Sc,Zr) precipitation kinetics. The precipitate size at a given temperature is not affected by the degree of Sc-supersaturation, while the number density showed a linear relation with the Sc-content in solution prior to ageing. In peak age condition, the Al3(Sc,Zr) volume fraction was close to the Al3Sc equilibrium volume fraction of a binary Al-Sc alloy.