Modellierung und Validierung zeitabhängiger mikrochemischer Prozesse in Aluminium Knetlegierungen
As a result of high cooling rates during the direct chill casting process of Al-Mn-Mg-Fe-Si alloys (typically AA3xxx series) Mn and Fe are quenched in a solid solution, due to their slow diffusion kinetics. Therefore the as-cast condition is far from thermodynamic equilibrium. One of the main goals of the industrial process of pre-heating is to precipitate Mn and Fe and to eliminate microsegregations.During heating of the as-cast ingot up to homogenisation temperature a variety of phases develop. Each of this phases can change its composition and its amount. From a metallurgical point of view the process is mainly dominated by nucleation, growth, dissolution and transformation of AlMn-dispersoids as well as other phases.In this work a statistical model was developed to describe this process within the framework of classical nucleation theory and the kinetics of growth and coarsening of precipitates. The ClaNG model (Classical Nucleation and Growth) predicts the precipitation kinetics during annealing 1xxx, 5xxx and in particluar 3xxx series alloys. The model is capable of describing the simultaneous nucleation, growth, coarsening and compositional changes of several types of spherical precipitates. To calculate the equilibrium phases, the chemical driving forces and the equilibrium concentrations, the commercial Gibbs energy minimizer ChemApp (GTT Technologies, Herzogenrath, Germany) and thermodynamic databases have been embedded. The main advantage of this strategy is that there is nearly no restriction on a special alloy system. The present algorithm is fast and therefore of particular interest for industrial applications.The experimental work focused on structural investigations of the influence of each alloying element. For a detailed characterisation of the metallurgical processes that determine microstructure evolution during pre-heating of an as cast-ingot, isothermal heat treatments with model alloys (AlMn1Mg1, AlMn1Mg1Fe0.45 and AlMn1Mg1Fe0.45Si0.2) as well as commercial AA3104 alloy in combination with real process data for pre-heating were carried out to validate the model.
info:eu-repo/classification/ddc/660, Technische Chemie, Computersimulation, Gefüge, Metall, Ausscheidung, Aluminium, Phasenumwandlung, Thermodynamik, simulation, microstructure, metals, precipitation, phase transformation
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