A model for co-clusters and their strengthening in Al–Cu–Mg based alloys: a comparison with experimental data

Abstract

A model for the thermodynamics of and strengthening due to Cu-Mg co-clusters in Al-CuMg based alloys is analysed and tested. The formulation uses a single interaction enthalpy between dissimilar alloying elements (e.g. Cu and Mg atoms in an Al-Cu-Mg based alloy) combined with the configurational entropy. The metastable solvus in Al-Cu-Mg based alloys is calculated. Recently published small angle X-ray scattering experiments, 3 dimensional atom probe and yield strength data on these type of alloys support the model. The small angle X-ray scattering and hardness experiments, as well as calorimetry experiments, are sensitive to the main free energy (or enthalpy) changes, which are dominated by Cu-Mg bonds formed by the dimers and the local electron densities related to these bonds. 3 dimensional atom probe is less sensitive to dimers, and will detect agglomeration of dimers to form larger clusters.

Untitled

“…clusters indicates strengthening effect that is the main strengthening mechanism in the alloy that contributes to high specific strengths and modulus. This finding confirms that there is direct relationship between strength and the amount of co-clusters formed [32]. precipitates is stable at 28.14nm before hot rolling and rises to 4µm during hot rolling then stabilizes at 27.628nm after hot rolling.…”

Analysis of nucleation and growth with the model for diffusion-controlled precipitation reactions based on the extended volume concept

“…6: for this reaction n appears to be constant at 2.5 independent of T tr /T s . Also this is consistent with the above interpretation as for these short range ordered structures the change in free energy is determined by the Cu-Mg bonds formed [39,40,44,45] and hence only continued formation (nucleation) of Cu-Mg bonds can reduce the free energy of the system.…”

“…the precipitate phase) in the alloy, T s . T s was estimated from solvus data of the Ni-Al system [37], data of the Pb-Ca system [38], TTT plots of precipitation in Al-Sc [25], the thermodynamic model for Cu-Mg co-clusters in Al-Cu-Mg alloys [39,40], the Fe-C system phase diagram, the Al-Si phase diagram and the estimated solvus of CrN by Weaver [24]. Data on T s thus obtained is included in Table 1.…”

Modelling and Simulation of Composition and Mechanical Properties of High Entropy Magnesium-based Multicomponent Alloy

“…Presence co-clusters indicates strengthening effect that is the main strengthening mechanism in the alloy that contributes to high specific strengths and modulus. This finding confirms that there is direct relationship between strength and the amount of co-clusters formed[32].…”