Precipitation in Stretched Al-Cu-Mg Alloys with Reduced Alloying Content Studied by DSC, TEM and Atom Probe

Abstract

Abstract. The hardening and microstructural evolution during ageing of a Al-1.2Cu-0.5Mg and a Al-1.2Cu-1.2Mg (at.%) alloy has been investigated. Artificial ageing at 150°C of stretched and naturally aged samples initially (up to about 48 h) leads to very limited further strengthening, but ageing at 190°C results a quick increase in strength. Detailed microstructural investigation using differential scanning calorimetry, transmission electron microscopy and three-dimensional atom probe demonstrated that hardening at 150ºC is mostly dominated by the formation of solute clusters with varying compositions and plate-like zones rich in copper at early stages of ageing (t<24h) and by the formation of S phase at the later stages of ageing. At higher 190ºC no zones or clusters form and the ageing is dominated by the formation of S precipitates.

A model for precipitation kinetics and strengthening in Al–Cu–Mg alloys

“…[29]). This allows us to apply a simplified precipitation sequence in the present work, which permits formulation of precipitation kinetics and strengthening model with transparent predictions [8,29]: α ss → Cu:Mg co-clusters → S phase precipitates This precipitation sequence is consistent with the two stage strengthening observed in these alloys with the initial stage attributed to the strengthening by the Cu:Mg co-clusters and the later stage attributed to the strengthening by the S phase precipitates [8,31,32].…”

VPPA welds of Al-2024 alloys: Analysis and modelling of local microstructure and strength

“…3D atom probe work has evidenced that in the present alloys room temperature hardening and hardening at 150 ºC is due to the formation of Cu-Mg coclusters [8,38,39], which become unstable at higher temperatures. Thus the endothermic effect up to about 230 to 250ºC is attributed mainly to the dissolution of these clusters [8,25,38]. For position 3, the dissolution of GPB2/S" phase will also contribute to the endothermic effect.…”

Activation energy determination for linear heating experiments: deviations due to neglecting the low temperature end of the temperature integral

“…17 indicates that ΔE/E is smaller than 0.3%, and hence neglecting of I(T o ) could not have influenced the determination of the activation energy significantly. In solution treated Al-Cu-Mg based alloys with compositions in the α+S phase field (at around 500K), linear heating will cause the formation Cu-Mg co-clusters (also termed GPB zones) [35,36,37,38] and S phase [39,40,41]. If the alloys are aged at low temperature to cause the formation of Cu-Mg coclusters, subsequent linear heating will cause the reversion of clusters prior to formation of S phase.…”