Piotr Warczok

Thermo-kinetic computer simulation of differential scanning calorimetry curves of AlMgSi alloys

Abstract The microstructure evolution in heat-treatable Al-alloys is characterized by a complex sequence of precipitation processes. These can be either endothermic or exothermic in nature and they can be investigated by thermal analysis. The individual peaks identified in a differential scanning calorimetry (DSC) analysis can be correlated to the nucleation, growth and dissolution of certain types of precipitates. Simultaneously, these data can also be obtained by thermo-kinetic simulation based on models implemented, for instance, in the software MatCalc. The simulations make use of information stored in thermodynamic databases, including stable and metastable phases. In the present work, a thermo-kinetic computational analysis of Al–Mg–Si DSC curves is carried out. The comparison with experimentally observed DSC signals for precipitation and dissolution of metastable GP-zones, β″, β′, as well as stable β-Mg2Si and Si precipitates provides a quantitative insight into the kinetics and sequence of precipitation during DSC probing. The combination of thermo-kinetic and experimental DSC analysis offers new possibilities in interpretation of DSC peaks with multiple metastable phases. In the present paper, we discuss the linking of the simulated precipitation sequence with the measured DSC signal. In addition, with the proposed methodology, a consistent set of parameters to describe the non-equilibrium kinetic parameters of a specific alloy system can be obtained, which can substantially aid in alloy and process development.

Agile Multiscale Modelling of the Thermo-Mechanical Processing of an Aluminium Alloy

The multiscale modelling of the behaviour of metal alloys during processing is often limited by the computing power required to run them. The Agile Multiscale Methodology was conceived to enhance the designing and controlling of complex multiscale models through an automatic run-time adaptation of its constitutive sub-models. This methodology is used to simulate the behaviour of an 6082 aluminium alloy during its thermomechanical treatment. The macroscopic deformation, the work-hardening and the state of precipitation are computed in different modules, allowing the coupling of several software solutions (DEFORMTM2D and

Analysis of Clustering Characteristics during early Stages of Cu Precipitation in bcc-Fe

Formation of coherent Cu precipitates in supersaturated ferrite (1.5 at.%Cu) at 500°C is simulated using the Monte Carlo method. Bond energies used in the atomistic simulation are calibrated on the mutual solubilities given on the Fe-rich and Cu-rich side of the Fe(bcc)-Cu(bcc) phase diagram. The spatial extension of the precipitate phase is defined on basis of a composition criterion of the nearest neighbor shells. Various definition conditions are examined in terms of resulting particle densities, mean radii and composition of the precipitates, as well as the composition profiles across the precipitate/matrix interface. The predictions of the simulations are compared with the experimental results from atom probe analysis as well as small angle neutron scattering.

Investigation of Cu precipitation in bcc-Fe – Comparison of numerical analysis with experiment

Abstract The precipitation of bcc-Cu clusters in ferrite was modelled using a multi-scale approach. From a combination of density functional theory and phonon density of states calculations with the cluster expansion technique, the solubilities of Fe and Cu in the corresponding bcc phases were obtained consistent with reported thermodynamic assessments. From these solubilities, effective bond energies were constructed for a Monte Carlo simulation of the precipitation kinetics. With a careful definition of the precipitate phase, based on the composition of the nearest neighbour shell, good agreement was observed with the experimental results obtained with 3D-atom probe and small angle neutron scattering for the Fe alloys with 1.0 and 1.5 at.% Cu annealed at 500 °C. The kinetics simulations on the continuum scale confirm the expected atomic mixing at the precipitate/matrix interface.

Simulation of Natural Aging in Al-Mg-Si Alloys

Natural aging during storage of Al-Mg-Si alloys at room temperature can significantly reduce the maximum strengthening potential (T6) during artificial aging and, therefore, is a key topic in aluminium research and industry. Many different strategies to understand and reduce the negative effect of natural aging have been investigated during the last decades, including analysis of different thermal pre-treatments and considering the effect of different microalloying elements. From these investigations, the vacancy evolution and the formation of clusters containing Mg and Si were found to be the governing aging mechanisms behind natural aging. In this work, we present a model to simulate and predict the behavior of these alloys when subjected to room temperature aging after solutionizing and demonstrate the effects of different thermal routes and chemical composition variations. In the implemented model, the evolution of excess quenched-in vacancies and the effect of solute vacancy traps are considered. Special emphasis is placed on co-cluster formation and its contribution to strengthening. The thermokinetic software MatCalc is used for the simulations and the results of the simulations are validated by experimental investigation.