Effects of pre-compression on the three-dimensional creep anisotropy of a hot-rolled Mg-4wt%Y binary alloy sheet

Abstract

The effects of pre-compression on the creep behaviors along rolling direction (RD), transverse direction (TD) and normal direction (ND) of a hot-rolled Mg-4wt%Y alloy sheet were investigated in this study. A valid and convenient method for enhancing creep resistance and a systematic research in understanding creep anisotropy were provided. The pre-compression was carried out at 298 K along TD and performed to a true strain of 0.07. The samples with pre-compression (PC) and without pre-compression (NPC) were labeled as NPC-RD, NPC-TD, NPC-ND and PC-RD, PC-TD, PC-ND, respectively. Compressive creep tests along different directions were carried out at 523 K under various applied stresses. The results showed that both NPC and PC samples had obvious a three-dimensional creep anisotropy. The sequence of creep resistance of NPC samples was ND > TD > RD. The dominant creep mechanisms of NPC-RD and NPC-TD samples were both cross-slip and twinning. While dislocation climb and pyramidal <c+a> slip dominated the creep of NPC-ND sample, resulting in the highest creep resistance among the three NPC samples. After pre-compression, the resultant sequence of creep resistance of PC samples was RD > ND > TD. Dislocation climb and frequent twin intersections became the dominant creep mechanisms and significantly enhanced the creep resistance of PC-RD sample. Due to detwinning, only a slight enhancement of creep resistance happened in PC-ND sample. The creep resistance in PC-TD sample perceptibly declined, because heavy cross-slip and stepped <c> dislocations accelerated the creep strain. Although the three-dimensional creep anisotropy still insisted in PC samples, pre-compression was manifested to be an excellent method for improving creep properties along the worst direction (RD).