  Al-Mg-Si alloys with total solute contents ranging from 0.8 to 1.4 wt.% were
solutionised, quenched and then artificially aged (AA) at 180 {\deg}C, after
which positron annihilation lifetime spectroscopy was applied to obtain
information about precipitation and vacancy evolution during preceding ageing.
Hardness and electrical resistivity measurements were carried out to complement
these measurements. AA was carried out in four different heating media, which
allowed for varying the heating rate from 2.4 K/s to 170 K/s. The main result
of the study is that there is a competition between vacancy losses and
precipitation. Any precipitation taking place during quenching or during
heating to the AA temperature helps to prevent vacancies from going to sinks
and allows them to assist in solute clustering. Higher solute content, slower
heating to 180 {\deg}C and natural pre-ageing before AA were found to have a
comparable effect.

Materials Science