Modelling dissolution of low melting point phases during the homogenisation of AA7020 aluminium alloy

The presence of low melting points (LMP) phases in the structure of 7XXX series aluminium alloys restricts the extrusion speed applicable and extrudate shape complexity. It is thus of great interest to understand and quantify the dissolution behaviour of the LMP phases during homogenisation at various temperatures and times before extrusion. In this research, an interface reaction limited (IRL) model was applied to predict the dissolution of the LMP phases in terms of the radius and volume fraction of the LMP phases as a function of homogenisation time and temperature. A value of 3.7 x 10(-6) m s(-1) was predicted for the kinetic coefficient of the interface reaction, which is in the typical range of kinetic coefficients for the interface reaction limited processes. The predictions of the volume fraction of the dissolved LMP phases from the model were verified experimentally using differential scanning calorimetry (DSC) and a good agreement was found.