Optimization of physical and mechanical properties of ultrafine-grained Al–Mg–Zr alloy for electrical purposes

For the ultrafine-grained (UFG) Al–0.95Mg–0.32Zr (wt.%) alloy structured by high-pressure torsion (HPT), a unique combination of strength (390 MPa), ductility ($\sim$10%) and electrical conductivity ($\sim$49% IACS – International Annealed Copper Standard) was achieved due to additional deformation-heat treatment (DHT), consisting of annealing at an elevated temperature of 230$^\circ$C for 1 h and a small additional deformation by HPT. The evolution of microstructure at both stages of DHT was studied. The analysis of the microstructure-property relationship showed that the achieved ductility is provided by the introduction of an additional dislocation density into the anneal-relaxed grain boundary (GB) structure and near-boundary regions as a result of DHT, as well as the formation of a significant fraction ($\sim$20%) of larger grains with a size of $>$ 900 nm in the UFG structure. The retention of strength after DHT at a level of $\sim$75% of the strength in the initial UFG state can be explained by the retention of a small average grain size (510 nm) and the formation of new Mg segregations at GBs.