Influence of pre-straining on creep behaviors of Mg-2Y alloy sheets

A compressive pre-straining of 0.05 was applied to two Mg-2Y alloy sheets with different initial textures along their normal directions. Creep behaviors of these sheets before and after the pre-straining were investigated at 493 K under stresses ranging from 20 to 100 MPa. The influence of pre-straining on creep behaviors was then discussed. The results show that the effects of pre-straining on creep behaviors of the two sheets are quite different. A profound strengthening effect of this pre-straining is observed on the creep resistance of the extruded sheet with creep strain decreased by half and steady strain rate reduced by 75% at most. By contrast, for the rolled sheet, the improvement of creep resistance by the pre-straining is negligible. The difference lies in the number of anomalous twins introduced by the pre-straining. After the pre-straining, considerable {10-12} anomalous twins have been introduced in the extruded sheet with a random initial texture, compared to the rolled one. Dislocation movements during the creep can be impeded by the large amounts of twins in the pre-strained extruded sheets, resulting in the obvious improved creep resistance. Meanwhile, different predominant dislocation mechanisms are found along different creep directions. Since a more excellent impeding effect of the twins is obtained on cross-slip, better improvement of the creep resistance can be achieved along the TD than along the ED of the pre-strained extruded sheet. (C) 2019 Elsevier B.V. All rights reserved.