Mechanical performance improvement of Al–Cu–Mg using various thermomechanical treatments

Abstract

A thermomechanical treatment (TMT) geared to stimulate solute atom clustering was devised to achieve a comprehensive balance of engineering properties in an Al–Cu–Mg alloy. The effect of the TMT on the microstructure and properties of an AA2524 like Al–Cu–Mg alloy were investigated using X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), and atom probe tomography (APT) along with tensile testing and fatigue crack growth testing. Our goal was to exceed threshold levels for fatigue crack growth (FCG) resistance, ductility and strength, using the T3 condition as a benchmark. During the TMT, dislocations and vacancies were introduced by solution treatment, quenching and pre-ageing, followed by asymmetric rolling. This enables short-circuit diffusive pathways that facilitate the formation of Mg–Cu co-clusters that effectively regulate the subsequent precipitation and influence mechanical properties. The contribution to critically resolved shear stress (CRSS) of these clusters of TMT alloys was significantly higher than the T3 state. It is proposed that Goss-grain orientations and shear textures introduced by the asymmetric rolling are also partly responsible for the enhancement of FCG resistance. The potential for solute clusters to contribute to fatigue properties is discussed in terms of the cyclic deformation shearing them, thus liberating their solute which can then bind with vacancies that would otherwise condense at the crack tip.