Effects of Yttrium Content on the Three-Dimensional Compressive Creep Anisotropy of Mg-Y Alloys

In this work, the compressive creep behaviors of hot-rolled pure Mg (0Y alloy) and various hot-rolled Mg-Y binary alloys (0.15Y, 1.5Y, 4.5Y, 7.5Y, and 10.5Y alloys) at 523 K were systematically studied under various applied stresses. These alloys all had an average grain size of ~100 μm. The loading directions were parallel to the rolling direction (RD), transverse direction (TD), and normal direction (ND). The creep behaviors were shown to exhibit an obvious dependence on the loading direction in the 0Y, 0.15Y, 1.5Y, and 4.5Y alloys. The creep resistance had a sequence of ND > TD ≥ RD in these alloys. The creep anisotropy of the alloys was caused by 〈a〉 dislocation cross-slipping from the basal plane to the prismatic plane and { $$ 10\bar{1}2 $$ } twinning dominating the creep along the RD and TD, while dislocation climb and pyramidal 〈c + a〉 slip prevailed along the ND. Compared to the 0Y, 0.15Y, and 1.5Y alloys, the more random basal texture in the 4.5Y alloy weakened the cross-slip and twinning along the RD and TD and triggered cross-slip along the ND, resulting in decreased creep anisotropy. For the 7.5Y and 10.5Y alloys, an approximate creep isotropy due to cross-slip and pyramidal 〈c + a〉 slip dominated the creep along all three loading directions. Moreover, compared to the 0Y alloy, the creep resistance was found to be slightly increased in the 0.15Y alloy and significantly increased with increasing the Y content above 1.5 wt pct, which can be attributed to solution strengthening and the promoted pyramidal 〈c + a〉 dislocations collaboratively increasing the creep resistance. The improved hindering effect on twinning also helped to increase the creep resistance along the RD and TD. In addition, dynamic precipitation strengthening assisted the increment of creep resistance in the 10.5Y alloy. Thus, the addition of concentrated Y in Mg alloys is a valid solution to eliminate the compressive creep anisotropy and simultaneously enhance the creep resistance.