Computer simulation of volume changes during phase transformation in Al-Si, Al-Cu, and Al-Mg-Si alloys

Abstract

In the last decades, aluminium alloys have been increasingly used in industries.<br />In car industries, they are used for the realisation of light weight panels for instance.<br />Due to their properties, aluminium alloys are very interesting materials. One of most interesting property of some aluminium alloys is the precipitation hardening. Aluminium alloys of the 2xxx (Al-Cu-(Mg)), 6xxx (Al-Mg-Si-(Cu)) and 7xxx (Al-Zn-Mg) series develop precipitates when they are submitted to a suitable heat treatment. Some of these precipitates strongly improve the mechanical properties of these alloys.<br />Even if this process is well-known, observed and used in industrial heat treatment since a long time, many things regarding the nucleation, growth, influence of these precipitates on thermo-mechanical behaviour remain unclear and controversial.<br />Among the testing methods that are used to inquire the precipitation process in aluminium alloys during artificial ageing, DSC and TMA are very popular.<br />In the last years, progress in simulation allowed developing computational tools relying on thermodynamics computation.<br />Through comparison between simulations and experiments, we expect to get interesting information on the precipitation process in aluminium alloys. The question of the volume changes is especially interesting because volume changes during heating up can be correlated to expansion of the matrix due to temperature plus precipitations and dissolution of phases with different molar volumes. This allows detecting the formation and checking kinetics of the precipitates.<br />This work aims to model and simulate the volume changes in alloys during heat treatments. It relies on literature in order to collect data on the various precipitates and their structure, dilatometry experiments and thermo-kinetics simulation. It highlights how volume changes can be modelled using the MatCalc software and how the model can be evaluated by comparing the experiments with simulations.<br />The focus is on three different systems. Al-Si binary system, precipitation hardenable Al-Cu and Al-Mg-Si systems. Additionally it contains a collection of some structural and molar volume of precipitates in Aluminium alloys for further development and refinement of volume change simulations.