Influence of second phase particles on the mechanical properties of a high solute Al-Zn-Mg alloy fabricated through laser powder bed fusion

A high solute 7xxx series aluminium alloy, Al-14Zn-3Mg (in wt%), was prepared using laser powder bed fusion (LPBF). To provide an insight into the correlation of second phase particles and mechanical properties, several heat treatment conditions were modelled with CALPHAD, and phase transformations were realised through in-situ characterisation techniques. It was revealed that the formation of T-phase (Mg₃₂(Zn, Al)₄₉) at 400 °C contributed to loss of ductility from the direct heat treatment of as-LPBF Al-14Zn-3Mg. However, the improvement in hardness of solutionised and peak aged Al-14Zn-3Mg was attributed to the formation of high volume fraction of η’ and η (MgZn₂) precipitates with low inter-precipitate spacing.