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 ?- and the S-phase solvus (using a regular-solution model), taking account of the capillary effect and ? 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) 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 aging conditions, achieving an accuracy of about 1 pct in predicting unseen conductivity data from this set of alloys