CREEP-BEHAVIOR AND DEFORMATION MICROSTRUCTURES OF MG-Y ALLOYS AT 550 K

Creep behavior and deformation substructures of Mg-Y binary alloys con taining 0.2-2.4 mol% Y have been investigated at 550 K under 50-200 MP a. Creep strength is remarkably improved by a small addition of yttriu m as compared with aluminum and manganese. Two stress regions are reco gnized based on the stress dependence of the minimum creep rate. The l ower-stress region, where the stress exponent n is about 5, correspond s to the H region (class M behavior) commonly observed in other solid solution alloys. The concentration dependence of solid-solution Mg-Y a lloys is similar to that of Mg-Al solid solution alloys: the apparent concentration exponent In is about - 2. The effect of the yttrium conc entration increases when the concentration exceeds 1.6 mol%. Transmiss ion electron microscopy reveals that the activation of the non-basal s lip systems is enhanced and dynamic precipitation occurs during creep deformation in a concentrated Mg-Y alloy. The high creep resistance ca n be correlated with two mechanisms, i.e. forest dislocation-hardening (work hardening) and dynamic precipitation of fine pseudo-equilibrium beta' phase on the dislocation lines during creep. (C) 1998 Elsevier Science S.A. All rights reserved.