The Effect of Scandium on Kinetics and Strengthening of Al-Mg <sub>2</sub>Si System Alloys in the Case of Ageing
The effect of Sc and Sc together with Zr additives on behaviour of wrought Al-Mg <sub>2</sub>Si system alloys during ageing has been investigated. The alloys had different contents of Mg and Si. Investigation indicated that after solution treatment followed by natural ageing the Sc additives resulted in alloy strengthening in the case of long-term ageing. During artificial ageing the Sc and Sc + Zr additives retarded strengthening of the Al-Mg <sub>2</sub>Si alloys and diminished hardness maxima. According to this, some decrease in strength properties of the alloys can be observed after ageing carried out under certain conditions. Transmission electron microscopy indicates that Sc can form with Si a ternary compound τ(Sc <sub>2</sub>AlSi <sub>2</sub>) appeared in a structure, but can exist also in the alloys as dispersed particles ScAl <sub>3</sub> with dissolved Zr, which are commonly observed in Al-Sc and Al-Mg-Sc alloys.