Micro-alloying effects of Ni on the microstructure and mechanical properties of an Al-Zn-Mg-Cu-Sc-Zr alloy

Abstract

Ni micro-alloying effects on the microstructure evolution and mechanical properties of an Al-Zn-Mg-Cu-Sc-Zr alloy have been thoroughly investigated, by the combined use of electron/atom microscopic characterization and first-principles calculations. A trace addition of 0.2 wt% Ni can induce a new primary phase of Al3(Ni, Cu) and further refine the grain size to 23 µm. A higher dislocation density with more sub-grains can be retained after hot extrusion and the subsequent solid-solution treatment. Ni could also promote the precipitation of η phase and improve its thermal stability, and in the meantime, Ni can segregate to Al GBs and directly enhance the GB binding. Eventually, even with a very low Cu/Mg atomic ratio (∼0.22), Ni micro-alloyed Al-Zn-Mg-Cu-Sc-Zr alloys can achieve remarkably high strength and thermal stability with an acceptable level of plasticity, as compared to most 7055 Al alloys.