Creep behaviors of a highly concentrated Mg-18 wt%Gd binary alloy with and without artificial aging

Abstract

In this work, a highly concentrated Mg-18 wt%Gd binary alloy was prepared and its tensile creep behaviors were studied. Both as-solution (AS) and as-aged (AA) samples were subjected to creep tests at 523 K under various stresses. The results showed that precipitate variants and sizes became similar in AS and AA samples during their secondary creep stages. Strain aging and artificial aging play equivalent roles in the strengthening effects on AS and AA samples. Dislocation climb composed by edge <a> dislocations was the dominant creep mechanism of AS sample, and dislocations bypassing precipitates strengthened AS sample limitedly. By contrast, cross-slip composed by basal <a> and prismatic <a> dislocations was the dominant creep mechanism of AA sample, and dislocations cutting precipitates strengthened AA sample obviously. Furthermore, compared to AS sample, a high density of precipitate-free zones (PFZs) were developed in AA sample during creep testing. These high-density PFZs then relieved local stress concentration and catalyzed a homogeneous stress distribution, which postponed the occurrence of creep rupture rather than accelerated it. Accordingly, AA sample had an increased creep resistance than that of AS sample at 523 K. This unexpected discovery that PFZs could contribute to the increase in creep resistance is believed to extend the application of the Mg-Gd alloys with vast potentials.