CALPHAD-informed phase-field modeling of grain boundary microchemistry and precipitation in high strength Al-Zn-Mg-Cu alloys

CALPHAD-informed phase field modeling, scanning transmission electron microscopy and atom probe tomography have been used to study the segregation, precipitation, and solute distribution in high strength Aluminium alloys (7xxx).

High strength Aluminium alloys (7xxx series) are important materials for a sustainable future, enabling weight reduction of electrical (and conventional) vehicles.

At the internal interfaces their advantage, i.e. their complex precipitation system, turns into a disadvantage, leaving large precipitation free zones around the grain boundaries. This creates high mechanical contrast and galvanic elements, obviously undesirable features.

In a recent collaboration we studied the segregation, precipitation, and solute distribution in these systems using CALPHAD-informed phase-field modeling, scanning transmission electron microscopy and atom probe tomography.

Fig. 1. APT reconstruction of the GB microchemistry and precipitation in the lab-cast model AA7050 alloy. (a) Atom maps of all elements in the as-quenched state, and (b) the corresponding composition profiles across the GB. (c) Distribution of GB precipitates after ageing for 2 h at 120 . (d) Distribution of GB precipitates, and (e) the corresponding compositions of the precipitate after ageing for 24 h at 120 . Al, Zn, Mg, and Cu are depicted in orange, dark cyan, dark yellow, and purple, respectively.
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