Effect of yttrium concentration on creep of Mg-Y alloys at 550K

Creep behavior of Mg-Y binary alloys with varus yttrium concentration have been examined at 550K. Creep strength is remarkably improved by the addition of yttrium. The concentration exponent, m of creep rate changes from similar to 2 (in the solid-solution range) to similar to 5 (in the two-phase range) with increasing yttrium concentration. TEM observations reveal that the non-basal, as well as the basal, slip systems are activated in the two-phase range, while the activation of the non-basal slip system is not obviously observed in the solid-solution range. Dynamic precipitation on dislocations during creep deformation occurs in the two-phase range. The strengthening due to the addition of yttrium is attributed to (i) solution-hardening, (ii) dynamic precipitation, and (iii) the forest dislocation density.