Hall–Petch Relationship in Electrically Pulsed Al–Zn–Mg Alloys

Abstract

Al-Zn-Mg solid solution alloys with average grain sizes of 18, 30, and 100 μm are obtained by a warm rolling-solution treatment. Based on the Hall-Petch and the Bailey-Hirsch relations, an inverse proportional model between dislocation density and grain size is proposed under the same plastic strain for nonpulsed alloys. The proportional coefficient is a function of the Hall-Petch slope k. The Hall-Petch relationship under different pulse parameters and heating conditions are obtained by controlling the temperature increase for samples using air cooling. The contribution ratio of drifting electrons (excluding Joule heating) to the variation of k is derived for different current densities. The divergence between the softening action of drifting electrons and Joule heating is discovered; i.e., drifting electrons are more inclined to lead to grain boundary softening than intragranular softening, whereas Joule heating has no obvious bias for either type of softening. Through mathematical derivation and experimental verification, it is found that the amount of dislocation reduction caused by an electric pulse has a negative correlation with grain size, leading to a change in k, which is of great significance to the theoretical development of electric pulse-assisted formation.