Solid solution hardening effect of aluminum on the creep deformaton of AZ91 magnesium alloy

Abstract

It has been previously shown that separate additions of 2% rare earth elements (RE) and 0.6% Zr to the AZ91 base alloy improve creep properties. However, in this investigation using impression creep method, it is shown that simultaneous addition of these elements not only cannot improve creep properties but also leads to its deterioration. According to the creep deformation mechanism of the base alloy and microstructural evidences, it is believed that this drop in creep resistance mainly stems from depletion of grain interiors and the areas adjacent to grain boundaries from aluminum solute atoms. Reduction of aluminum content as solute atoms is due to the great affinity of RE and Zr atoms for aluminum. This leads to the weakening of Al solute atoms role as obstacles against dislocation movement, even though the volume fraction of the thermally stable particles tends to be high.