Microstructural evolution during ageing of Al-Cu-Li-x alloys

TL;DR

This study uses atom probe tomography to analyze the microstructural evolution of AA2198 alloy during ageing, revealing details about phase nucleation, precursor phases, and solute segregation that inform the understanding of strengthening mechanisms.

Contribution

It provides new insights into the nucleation mechanism of T1 phases and the role of solute segregation in Al-Cu-Li alloys during ageing.

Findings

T1 precursor phases are present from early ageing.

Segregation of Ag and Mg to T1 interfaces was observed.

Connected dislocation structures influence phase nucleation.

Abstract

In this study atom probe tomography was used to investigate the microstructure of AA2198 (Al-1.35Cu-3.55Li-0.29Mg-0.08Ag) over a range of ageing conditions to examine the evolution of phases in the alloy, in particular aiming to reveal the nucleation mechanism of the strengthening T1 phase, which has been under debate for decades. T1 precursor phases were observed from early ageing, a significant number of which were connected to solute-enriched dislocations. Ag and Mg segregation to T1 interfaces was convincingly observed when the plates were oriented perpendicular to the probing direction, which is the condition under which the spatial resolution of the atom probe data is highest.