A model for the electrical conductivity of peak aged and overaged Al-Zn-Mg-Cu Alloys

A physically-based model for the electrical conductivity of peak aged and overaged Al-Zn-Mg-Cu (7xxx series) alloys is presented. The model includes calculations of the η and the S phase solvus (using a regular solution model), taking account of the capillary effect and η coarsening. It takes account of the conductivity of grains (incorporating dissolved alloying elements, undissolved particles and precipitates) and solute depleted areas at the grain boundaries. Data from optical microscopy, differential scanning calorimetry (DSC), scanning electron microscopy (SEM) along with energy dispersive X-ray spectrometry (EDS), and transmission electron microscopy (TEM) are consistent with the model and its predictions. The model has been successfully used to fit and predict the conductivity data of a set of 7xxx alloys including both Zr containing alloys and Cr containing alloys under various ageing conditions, achieving an accuracy of about 1% in predicting unseen conductivity data from this set of alloys.