On the heat treatment and mechanical properties of a high solute Al–Zn–Mg alloy processed through laser powder bed fusion process

High strength alloys in the Al–Zn–Mg system are primarily strengthened through artificial ageing by the formation of precipitates that are rich in Mg and Zn. In this work, a high solute Al–Zn–Mg alloy with 14 wt% Zn and 3 wt% Mg was prepared using the laser powder bed fusion process (LPBF). Heat treatment of Al–14Zn–3Mg revealed the presence of a high volume fraction of η’ and η-Mg(Zn, Al)₂ precipitates in the Al-matrix, accompanied by a compromise of mechanical properties. This was elucidated in the context of microstructure – strength relationship, where the results demonstrate a loss of mechanical properties in aluminium alloys when the area fraction of second phases exceeds ~50%. This study is a discrete effort towards revealing the critical solute limits of Zn and Mg in aluminium that are imperative to achieve high strength through second phase particles – a fundamental concept that maybe exploited in the future design of high strength Al-alloys through additive manufacturing.