Although the potential of high–specific strength 7xxx series (Al-Zn-Mg) aluminium wrought alloys for use in safety-relevant automotive parts is well known, they are still rarely used in automotive applications. One reason is their limited extrudability to complex shapes due to high alloying contents and nanoscale dispersoids that form during homogenization, leading to limited hot forming behaviour. The adaptation of industrially relevant homogenization regimes can help to overcome this challenge by controlling the precipitation of the dispersoids, positively impacting final product properties (microstructure and strength in T5).

In this study, different investigations have been performed, aiming to optimize the extrudability by tailored precipitation of nanoscale dispersoids in the alloy EN AW-7108A. We conducted different homogenization heat treatments, lab-scale extrusion, and artificial ageing to achieve T5 condition. For characterizing the as-cast, homogenized, and extruded states, we performed extensive microstructural investigations, differential scanning calorimetry, and warm forming tests. Special emphasis was laid on studying the effect of different homogenization regimes on the formation of nanoscale Al3Zr-dispersoids using scanning and transmission electron microscopy as well as atom probe tomography.

The results provide relevant insights towards the goal of finding an optimized alloy composition and homogenization parameters to achieve good extrudability and high strength after artificial ageing.