Creep behavior and deformation microstructures of Mg–Y alloys at 550 K

Creep behavior and deformation substructures of Mg–Y binary alloys containing 0.2–2.4 mol% Y have been investigated at 550 K under 50–200 MPa. Creep strength is remarkably improved by a small addition of yttrium as compared with aluminum and manganese. Two stress regions are recognized based on the stress dependence of the minimum creep rate. The lower-stress region, where the stress exponent n is about 5, corresponds to the H region (class M behavior) commonly observed in other solid solution alloys. The concentration dependence of solid-solution Mg–Y alloys is similar to that of Mg–Al solid solution alloys: the apparent concentration exponent m is about −2. The effect of the yttrium concentration increases when the concentration exceeds 1.6 mol%. Transmission electron microscopy reveals that the activation of the non-basal slip systems is enhanced and dynamic precipitation occurs during creep deformation in a concentrated Mg–Y alloy. The high creep resistance can be correlated with two mechanisms, i.e. forest dislocation-hardening (work hardening) and dynamic precipitation of fine pseudo-equilibrium β′ phase on the dislocation lines during creep.