Mesoscale Modeling of Dendritic Growth During Directional Solidification of Aluminium Alloys

Abstract

The development of materials based on metallic alloys with specific properties requires controlled solidification processes. Indeed, materials properties depend strongly on the microstructure. In the past few decades numerous studies on microstructure development have been reported. The growing demands of industry enhance research constantly. To get a better control on the microstructure and therefore the properties of materials, it is necessary to understand phenomena which occur in the solidification processes.

In the study of metallic alloys solidification (opaque system), one of the major difficulty is the visualization of the microstructure evolution during solidification. A method was developed using synchrotron radiation at the end of last century. This study aims at processing data from in situ and real time observations carried out at ESRF, comparing them with existing theories and developing a model to describe the experiments and understand phenomena.

The presentation is divided in two main parts.

First, the relevant scientific background is presented. A literature review of the theories of microstructure formation is reported in order to establish a basis of the present study. A brief presentation of ESRF where experiments were carried out, the experimental apparatus and sample preparation is described. Several samples of different compositions of aluminiumcopper have been prepared. Data processing allows the extraction of different relevant information about solute concentration, grain motion, tip growth, grain envelope during solidification.

The second part is a presentation of the results in the form of two separate scientific publications and one report. The work concerns a model simulating the experiments. The first paper focuses on the grain motion in grain refined alloys and analyses the effect of the sample geometry. The second paper presents a model to describe columnar dendritic growth at a mesoscopic scale. The different physical parameters of the experimental system are taking into account. This model is validated for different analytical solutions and is compared to the experiments. The predicted results as grain envelopes, height of the mushy zone, solid fraction and solute concentration are in good agreement with the experimental observations. Finally, the report illustrates the effect of gravity driven melt flow and presents an extension of the previous model to include melt flow. Additional research is necessary to improve and validate the model.