Dissolution of Precipitates During Solution Treatment of Al-Mg-Si-Cu Alloys

A model combining classical diffusion-controlled dissolution equation for a single spherical particle and Johnson–Mehl–Avrami-like equation is used to deal with dissolution process for different kinds of precipitations (Si, Mg₂Si, Q(Al_1.9Mg_4.1Si_3.3Cu)) in Al-Mg-Si-Cu alloys. The results reveal that the dissolution time of precipitates increases with increasing their sizes and solute concentrations in the alloy matrix; for the same size and concentration, their dissolution times follow Si > Q(Al_1.9Mg_4.1Si_3.3Cu) > Mg₂Si. Two precipitates (Mg₂Si and Al_1.9Mg_4.1Si_3.3Cu) with a size of about 700 nm were obtained in a cold rolled Al-Mg-Si-Cu-Zn alloy, and the complete dissolution time is about 15 seconds, which is basically the same as the calculated time by the developed model. The theoretical prediction of dissolution time can be greatly used to design solution treatment and thermomechanical processing parameters of Al-Mg-Si-Cu alloys.